Exploiting the S4-S5 Specificity of Human Neutrophil Proteinase 3 to Improve the Potency of Peptidyl Di(chlorophenyl)-phosphonate Ester Inhibitors: A Kinetic and Molecular Modeling Analysis

Article abstract of DOI:10.1021/acs.jmedchem.7b01416

The neutrophilic serine protease proteinase 3 (PR3) is involved in inflammation and immune response and thus appears as a therapeutic target for a variety of infectious and inflammatory diseases. Here we combined kinetic and molecular docking studies to i

Full text of DOI:10.1021/acs.jmedchem.7b01416

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Article
Exploiting the S4-S5 specificity of human neutrophil proteinase 3
to improve the potency of peptidyl di(chlorophenyl)-phosphonate
ester inhibitors: a kinetic and molecular modeling analysis
Carla Guarino, Natalia Gruba, Renata Grzywa, Edyta Dyguda-Kazimierowicz, Yveline Hamon,
Monika Legowska, Marcin Skore#ski, Sandrine Dallet-Choisy, Sylvain Marchand-Adam, Christine
Kellenberger, Dieter E. Jenne, Marcin Sie#czyk, Adam Lesner, Francis Gauthier, and Brice Korkmaz
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jmedchem.7b01416 • Publication Date (Web): 14 Feb 2018
Downloaded from http://pubs.acs.org on February 15, 2018
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Exploiting the S4-S5 Specificity of Human Neutrophil Proteinase 3 to Improve
the Potency of Peptidyl Di(chlorophenyl)-Phosphonate Ester Inhibitors:
A Kinetic and Molecular Modeling Analysis
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Carla Guarino1§, Natalia Gruba2§, Renata Grzywa3, Edyta Dyguda-Kazimierowicz4, Yveline
Hamon1, Monika Legowska2, Marcin Skoreński3, Sandrine Dallet-Choisy1, Sylvain
Marchand-Adam1, Christine Kellenberger5, Dieter E. Jenne6, Marcin Sienczyk3, Adam
Lesner2, Francis Gauthier1 and Brice Korkmaz1*
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§ These authors contributed equally to this work
1INSERM U-1100, “Centre d’Etude des Pathologies Respiratoires” and Université François Rabelais,
37032, Tours, France; 2University of Gdansk, Faculty of Chemistry, Wita Stwosza 63, 80-308 Gdansk,
Poland; 3Wroclaw University of Science and Technology, Faculty of Chemistry, Division of Medicinal
Chemistry and Microbiology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland; 4Wroclaw
University of Science and Technology, Faculty of Chemistry, Advanced Materials Engineering and
Modelling Group, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland; 5CNRS-Unité Mixte de
Recherche (UMR), Architecture et Fonction des Macromolécules Biologiques,13288 Marseille,
France; 6Institute of Lung Biology and Disease, German Center for Lung Research (DZL),
Comprehensive Pneumology Center, 81377 Munich and Max Planck Institute of Neurobiology, 82152
Planegg-Martinsried, Germany
Running title: Phosphonate inhibitors of PR3
Abstract
The neutrophilic serine protease proteinase 3 (PR3) is involved in inflammation and immune
response and thus appears as a therapeutic target for a variety of infectious and inflammatory diseases.
Here we combined kinetic and molecular docking studies to increase the potency of peptidyl-diphenyl
phosphonate PR3 inhibitors. Occupancy of the S1 subsite of PR3 by a nVal residue and of the S4-S5
subsites by a biotinylated Val residue as obtained in biotin-VYDnVP(O-C6H4-4-Cl)2 enhanced the
second order inhibition constant kobs/[I] towards PR3 by more than ten times (kobs/[I] = 73000 ± 5000
M-1s-1) as compared to the best phosphonate PR3 inhibitor previously reported. This inhibitor shows
no significant inhibitory activity toward human neutrophil elastase and resists proteolytic degradation
in sputa from cystic fibrosis patients. It also inhibits macaque PR3 but not the PR3 from rodents and
can thus be used for in vivo assays in a primate model of inflammation.
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INTRODUCTION
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Polymorphonuclear neutrophil phagocytes are characterized by the presence of abundant
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intracytoplasmic granules rich in anti-microbial peptides and proteins involved in innate immunity.
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Azurophilic granules also store four neutrophil serine proteases (NSPs): proteinase 3 (PR3), elastase (NE),
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cathepsin G (CG) and neutrophil serine protease 4 (NSP-4) which are released into the environment in
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response to inflammatory stimuli.
An excess of proteases may be released however during chronic
inflammation which disrupts the protease-protease inhibitor balance and accelerates proteolysis of the
extracellular matrix. 4, 5 The administration of exogenous inhibitors targeting these proteases may thus be
an excellent therapeutic strategy to fight inflammation. 5, 6 Though the total amount of PR3 in neutrophils
is similar to that of NE or CG, its activity is by far less controlled by endogenous inhibitors. 7 Indeed there
is no specific endogenous inhibitor of human PR3 (humPR3) and one of its more potent inhibitors, alpha-
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1-proteinase inhibitor (α1PI), interacts about 100 times less rapidly with humPR3 than with humNE.
Further, the pathophysiological role of humPR3 is less well understood than that of the related humNE and
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CG. Its function as autoantigen in granulomatosis with polyangiitis
and its likely involvement in
neutrophil apoptosis 11 makes it different from its closest homologue humNE.
humPR3 closely resembles humNE structurally and functionally with a highly conserved catalytic
triad (His57, Asp102 and Ser195 residues (chymotrypsinogen numbering)) located between two similar
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domains each comprising a six-stranded β-barrel.
Its pI however is somewhat less basic than that of
humNE. 5, 13 Several residues on the loops surrounding the protease active site assist the catalytic process.
Most importantly, the backbone amide hydrogens of Gly193 and Ser195 that define the oxyanion hole and
are located near the carbonyl group of the substrate’s scissile bond, stabilize the developing partial charge
on the tetrahedral intermediate during catalysis. 14
The structural analysis of the active site of humPR3 and humNE showed that the distribution of
charged residues close to the substrate binding site (99 loop, 60 loop, 37 loop and autolysis loop) of these
two proteases differs notably. 15 Thus, humPR3 contains three charged residues Lys99, Asp61 and Arg143
in the active site region. 12 The S1 binding pocket of humPR3 and humNE is hemispherical, therefore both
preferentially accommodate small hydrophobic residues at the P1 position (according to the nomenclature
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of Schechter and Berger (Schechter and Berger, 1967)). 7, 13 The S2 subsite of humPR3 differs from that of
humNE by the presence of a solvent accessible Lys at position 99, favoring accommodation of negatively
charged or polar P2 residues in the deep S2 subsite of PR3. 12 The Leu99 residue in humNE makes the S2
pocket more hydrophobic. The Lys99 of humPR3 is conserved in the PR3 of higher primates and many
artiodactyls, but not in PR3 of new world monkeys and rodents, whereas the Leu99 of humNE is highly
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conserved in many other species. This makes the PR3 specificity of these latter species different from
that of humPR3 and explains that rodents are not an appropriate animal model for studies related to the
biological activity of humPR3. Another critical residue that makes the specificities of humPR3 and
humNE different is that at position 217 in the vicinity of the S4 subsite where an Ile in humPR3 is replaced
by an Arg in humNE. 16, 17
We have designed and synthesized selective peptidyl-diphenyl phosphonate inhibitors based on
these structural differences between humPR3 and humNE using the sequence of an optimized peptide
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substrate of PR3. Phosphonate inhibitors are peptide based transition state irreversible inhibitors which
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form transition-state-resembling complexes with serine proteases.
The inhibition is initiated by the
formation of a noncovalent enzyme-inhibitor complex which upon the nucleophilic attack of the Ser195
on the phosphorus atom loses one aryloxy group forming an initial, irreversible covalent complex (Figure
1). Further aging followed by hydrolysis of a second ester group leads to the formation of an aged
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covalent protease-inhibitor complex stabilized by the oxyanion hole.
Phosphonate inhibitors are
chemically stable inhibitors that block selectively serine proteases at low concentration under acidic or
neutral conditions. 22 Phosphonate inhibitors were designed and developed by anchoring of the serine trap
to the recognition sequence derived from a peptidyl substrate of the target protease (Figure 1). These
inhibitors which interact covalently with the Ser195 of the catalytic triad can also be used as activity-based
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probes (ABP) to visualize membrane-bound or intracellular, proteolytically active, serine proteases.
Several peptidyl-diphenyl phosphonate inhibitors of humPR3 have been developed but all were more
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potent toward humNE
until we synthesized the first selective chlorodiphenyl phosphonate humPR3
inhibitors, the N-biotinylation of which allows to use them ABP to visualize active humPR3 in biological
samples. 18
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Application of PR3 inhibitors as therapeutic tools requires that they easily reach and interact with
their target protease with great specificity, they resist degradation during their administration and in situ,
and their half-life in the organism is significant. Using inhibitors as therapeutic tools also requires that a
relevant animal model is available for preclinical studies. In this work, we first designed and developed
new Biotin-peptidylP(O-C6H4-4-Cl)2 inhibitors with improved potency of action toward humPR3, to use
them as versatile pharmacological tools for assessing protease function in vivo. We focused on improving
the rate constant for inactivation (kobs/[I]) by molecular docking trials and on analyzing structure-activity
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relationships (SAR) to optimize efficacy at a very-low-dose and thus make the resulting compound
effective for a pharmacological application. Since PR3 from rodents retain a substrate specificity that
differs from that of human 27, we then looked for a relevant in vivo model of inflammation and tested
phosphonate inhibitors on the PR3 from Macaca fascicularis.
RESULTS
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Stabilizing properties of a biotinylated N-terminal P4 residue in PR3 substrates and inhibitors
Replacing the N-terminal acetyl group by biotin (Bt) in Ac-PYDAP(O-C6H4-4-Cl)2 (1) to give Bt-
PYDAP(O-C6H4-4-Cl)2 (2) significantly improved the kobs/[I] value 18 (4168 M-1s-1 vs 154 M-1s-1) (Table 1)
and significantly improved the Ki value of the initial non covalent complex (21 nM vs 3600 nM) (Table
2). Accordingly, the substitution of the N-terminal acetyl group by a biotin in the paranitroanilide (pNA)
substrate Ac-PYDA-pNA, increased the specificity constant kcat/Km by ~6 fold (Table 3). We employed
a computational docking approach to explain how biotin could modulate the interaction between Bt-
PYDAP(O-C6H4-Cl)2 and the active site of PR3 (Figure 2A, B). The lowest energy binding mode obtained
in the docking studies of 2 with humPR3 revealed that the biotin moiety is located in the S5 pocket limited
by the Lys99, Phe166, Cys168, Arg177 and Ile217 residues (Figure 2B). The entrance into this pocket is
guarded by the Lys99 side chain with its ε-amino group creating a hydrogen bonding with the carbonyl
oxygen of the Bt-Pro4 amide bond. This interaction would facilitate the correct orientation of both Pro4
and biotin in the S4 and S5 binding sites, respectively. The arrangement of Phe166, Cys168, Arg177
residues in the S5 subsite creates the cavity that accommodates the biotin heterocyclic rings (Figure 2B).
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The stabilizing role of biotin was confirmed introducing a polyethylene glycol [PEG]2 spacer between the
P4 residue Pro and biotin (Bt-[PEG]2-PYDAP(O-C6H4-4-Cl)2 (3) which resulted in a dramatic fall of the
kobs/[I] (Table 1). The docking model shows that the length of the biotin moiety is optimal for the binding
in the S5 pocket and any spacer between the Pro4 and biotin would not improve the interaction. A biotin at
P5 was thus retained for the construction of new inhibitors with a modified peptidyl sequence.
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Influence of the P4 residue on the inhibitory activity of Bt-peptidylP(O-C6H4-4-Cl)2 phosphonate
inhibitors
The computational docking study showed that the P4 residue Pro in 2 was close to solvent
accessible hydrophobic Trp218 in PR3 (Figure 2B). We replaced the P4 Pro by Val (4), Leu (5), Ile (6)
and norleucine (nLeu) (7) to tentatively optimize the interaction with the PR3 hydrophobic patch build by
residues Phe166, Ile217, Phe224 and possibly with Trp218. While Leu or Ile at P4 position decreased the
inhibitory activity toward PR3, the presence of nLeu or Val improved the inhibitory activity by ~2 and ~4
times respectively (Table 1). Accordingly, the specificity constant kcat/Km of the pNA substrate Bt-
VYDA-pNA was also improved (Table 3). Whatever the substitution at P4 in phosphonate inhibitors was
the resulting compound retained no significant inhibitory activity toward humNE though this protease also
prefers a hydrophobic residue at this position. Because the S4 subsite is composed mainly by side chains
of Trp218 and Ile217 and the distinctly hydrophobic area (Phe166, Phe224) span beyond this position, we
decided to probe the existence of interactions by substitution nLeu by nLeu(O-Bzl) at P4 in 7 (8).
However, this resulted in more than 10 times lower kobs/[I] value (Table 1). Moreover, the molecular
docking model did not confirmed the interaction between nLeu(O-Bzl) and, as mentioned above, a distant
hydrophobic area. In fact, the P4 side chain of 8 makes contact mainly with Trp218 (Figure 2C). The
comparison with the 2 model (Figure 2B) indicates that the introduction of more sizable nLeu(O-Bzl)
group at P4 does not alter the overall mode of binding but affects the placement of inhibitor backbone at
the S4 subsite thus preventing hydrogen bond formation between Lys99 and the carbonyl oxygen of the
Bt- nLeu(O-Bzl) amide (Figure 1C).
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Influence of the P1 and P4 residues on the efficacy of Bt-peptidylP(O-C6H4-4-Cl)2 phosphonate
inhibitors
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Unlike the S2 subsite of PR3 that preferentially accommodates negatively charged P2 residues and
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is thus essential to confer PR3 selectivity 15, the S1 subsite in PR3 may accommodate a variety of residues
including norvaline (nVal) and aminobutyric acid (Abu) among the favorites. We substituted the P1 alanyl
residue in the parent inhibitor (2) by Abu and nVal. Bt-PYDAP(O-C6H4-4-Cl)2 (2) and Bt-PYDAbuP(O-
C6H4-4-Cl)2 (9) showed similar efficacy toward PR3 (Table 1). However, Bt-PYDnVP(O-C6H4-4-Cl)2 (10)
was ~4.5 times more potent than 2.
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As expected the substitution of Pro by Val at P4 in 10 (11) significantly improved the kobs/[I]
value providing the best inhibitor of the series with a kobs/[I] = 73000 ± 5000 M-1s-1. This 20 fold increase
as compared to 1 resulted from a decrease in the Ki value of the initial equilibrium between PR3 and Bt-
VYDnVP(O-C6H4-4-Cl)2 (11) and an increase of the first order rate constant k2 producing the final
covalent complex (Table 2). Combining Val at P4 and nVal at P1 in the pNA substrate Bt-VYDnV-pNA
also significantly increased the specificity constant towards PR3 (Table 3).
The computational docking approach employed to examine the interaction between Bt-
VYDnVP(O-C6H4-4-Cl)2 and humPR3 (Figure 3A) revealed that for the lowest energy pose the overall
mode of enzyme-inhibitor binding resembles the one obtained for Bt-PYDAP(O-C6H4-4-Cl)2 (2). The
biotin aliphatic chain interacts with the hydrophobic surface of S5 subsite while the biotin rings extend
into the terminal cavity of this subsite in the manner observed with Bt-PYDAP(O-C6H4-4-Cl)2. For both
models the P4 residue of inhibitor is located at the narrow subsite with the Trp218 on one side and the
Lys99 on the other. Therefore increased inhibitory potency observed for derivatives with Val instead of
Pro at P4 may be due to an improved flexibility of this region upon enzyme-inhibitor binding. The ε-
amino group of Lys99 forms hydrogen bonds with Bt-Val4 amide carbonyl oxygen as well as Asp2
carboxyl group. Additionally, quantum chemical calculations of interaction energy revealed that Lys99
residue contributes the most to binding of Bt-Val4 portion of the inhibitor, as the value of the interaction
energy due to the presence of this particular residue amounts to -16.6 kcal/mol (Table 4). Attracting
interactions between Bt-Val4 tail of 11 and PR3 residues were also found for Phe166 and Val216 (-3.8
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and -1.6 kcal/mol, respectively). Except for Ile217, Trp218, and Phe215 residues that appear to exert
unfavorable influence in terms of Bt-Val4 binding, the remaining PR3 residues promote Bt-Val4 binding
with the interaction energy not exceeding -1 kcal/mol. It should be pointed out that excessively repulsive
interactions associated with some residues probably arise from the lack of quantum chemical refinement
of the binding poses obtained from docking simulations, as empirical force field-based methods often
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employed throughout the docking procedures tend to introduce shortened intermolecular contacts. The
location of the biotin rings into the S5 binding site prevents recognition of all these compounds by
extravidin by Western blotting (WB) under non-denaturating/reducing conditions (not shown).
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Stability of Bt-VYDnVP(O-C6H4-4-Cl)2 (11) in a biological environment
We then tested the properties of 11 in sputa from patients with cystic fibrosis (CF) and measured
humPR3 activities of sputum samples before and after incubation with 11 (5-10 nM final). A 1 nM
humPR3 concentration was estimated in these samples by comparison with the rate of hydrolysis of the
ABZ-VADnVADYQ-EDDnp substrate. Cleavage of the humPR3 substrate was totally inhibited after
incubation for 20 min at 37°C with 11 (Figure 3B), while humNE activity remained unchanged (not
shown). Inhibitor 11 was also successfully used to selectively label proteolytically active humPR3 in CF
sputum and in a lysate of purified human blood neutrophils (Figure 3C). Additionally, we showed that
inhibitor 11 preserved full inhibitory activity and resisted degradation when it was mixed with CF sputum
for 2 h at 37°C as shown by high performance liquid chromatography (HPLC) (Figure 3D).
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Characterization and inhibition of macaque PR3 (macPR3) by phosphonate inhibitors in
purified neutrophil lysates
Protein sequences alignment of humPR3 and macaque PR3 (Macaca fascicularis), shows that they
are 86% identical, and they differ by only 28 residues. Their substrate binding site is very similar and
critical residues Lys99, Arg143, Ile217 that confer high selectivity to humPR3 are conserved in macPR3
(Figure 4A, B). We thus hypothesized that, unlike PR3 homologues in rodents, macPR3 will be
efficiently inhibited by peptide-based phosphonate inhibitors designed for humPR3. All phosphonate
inhibitors of humPR3 reported above were able to inhibit macPR3. As observed for humPR3, biotinylated
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inhibitors were more efficient than acylated inhibitors at inhibiting macPR3 (1, Ac-PYDAP(O-C6H4-4-
Cl)2, kobs/I= 55 ± 4 M-1s-1; 2, Bt-PYDAP(O-C6H4-4-Cl)2, kobs/I= 1985 ± 215 M-1s-1; 11, Bt-VYDAP(O-
C6H4-4-Cl)2, kobs/I= 36480 ± 3350 M-1s-1) but their overall potency was somewhat lesser than that
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recorded for humPR3 (Table 1). The inhibition of macPR3 with 11 is shown in Figure 3C.
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To further examine binding preferences of 11 against human and macPR3 proteases and
interaction energy values between Bt-Val4 fragment of the inhibitor and PR3, binding sites were
compared for particular residues representing S5 binding pocket (Table 4). Lys99, the most important
residue promoting inhibitor binding of humPR3, seems to exert also the largest influence in terms of the
analogous interaction with macPR3. However, the corresponding binding energy value is less significant
in the case of macPR3-inhibitor complex compared to interaction with humPR3 (-10.0 versus -16.6
kcal/mol; Table 4). Another substantial difference in binding energy values concerns repulsive interaction
due to the presence of Phe215 residue. Unfavorable interaction characterizing humPR3-inhibitor complex
(5.5 kcal/mol) amounts to 24.2 kcal/mol in the corresponding macPR3 Phe215-inhibitor complex (Table
4). The remaining repulsive interactions associated with Ile217 and Trp218 are retained in the case of
macPR3 inhibition, despite the substitution of Trp218 by an arginine residue. Interestingly, three out of
five substitutions that involve PR3 residues in the vicinity of Bt-Val4 inhibitor fragment do not seem to
modulate binding potency of 11 against human and macPR3 homologs. The more substantial changes
related to residue substitution accompany the change of Phe166 to leucine and Gly219 to glutamate.
However, these substitution-induced changes in binding energy cancel each other out, as the interaction
energy value increased by 3 kcal/mol as a result of the Phe166Leu substitution is decreased by the same
extent upon the Gly219Glu substitution. Overall, the differences in inhibitor binding by human and
macPR3 appear to arise from decreased attractive interaction with Lys99 and increased repulsion with
Phe215 residues. Since conformation and spatial placement of these two residues is essentially identical in
both complexes, the observed changes in binding energy appear to arise from slightly different positioning
of the Bt-Val4 portion of the inhibitor molecule due to substitutions present in the macPR3 S4 and S5
subsites.
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DISCUSSION
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Evidence has now accumulated that the neutrophilic serine protease humPR3 acquired specific
pathophysiological properties and non-redundant functions in spite of its close resemblance to humNE. 5, 29
Indeed it slightly differs from the latter by its spatiotemporal localization 30, its substrate specificity, its
sensitivity to natural inhibitors, all factors that taken together explain its specific function as an
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autoantigen in granulomatosis with polyangiitis and its probable involvement in cell apoptosis.
Controlling the proteolytic activity of this protease specifically, e.g. by protease inhibitors, is a mean to
better understand its biological function. But all physiological inhibitors of humPR3 preferentially target
humNE. It is only recently that we and others began to synthetize chemical inhibitors that selectively
target the humPR3 active site. 7 The specificity of serine proteases is determined by their substrate binding
sites that are located on both sides of the cleaved peptide bond. We used a substrate-based approach to
develop serpin-like irreversible inhibitor (SerpinB1(STDA/R) and azapeptide (azapro-3), reversible
[31]
inhibitor that selectively inhibit PR3.
Such inhibitors however cannot be used as ABP to visualize
active humPR3 in biological fluids or in cells and tissues. We recently developed a series of N-terminally
biotinylated peptidyl-diphenyl phosphonate inhibitors that allow the detection of humPR3 at the cell
surface and inside cells. 18 These are transition state analogs, irreversible inhibitors that interact with non-
prime subsites of the target serine protease to form “phosphonylated” enzymes. Protease-inhibitor
complexes show a remarkable stability due to the similarity of the phosphorus atom with the tetrahedral
intermediate formed during peptide bond hydrolysis. Though chemically stable in blood samples, their
pharmacological use requires that they interact rapidly with their target protease to be effective at low
concentrations. We have further investigated the non-prime specificity of humPR3 to develop more potent
di(chlorophenyl)-phosphonate ester inhibitors that could be used as molecular probes to control humPR3
activity.
We previously showed that the S2/P2 specificity was essential to discriminate between humPR3
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and its close homologue humNE.
Lys99 in humPR3 is key residue to explain the preferential
5, 7
accommodation of negatively charged or polar residues at P2.
Thus selective humPR3 substrates or
peptide sequences selectively cleaved by humPR3 all contain a negatively charged or a polar residue at
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position P2. SerpinB1(STDA/R) and azapro-3 that selectively inhibit humPR3 contain a negatively
charged residue (Asp) at P2 position. However, humPR3 may accommodate different residues at P1 and
P4 as confirmed by molecular modeling studies. The S1 binding pocket of humPR3 is more accessible
and spacy than that of humNE and can accommodate not only the Ala or Abu side chain but also
methionine, valine, nVal which was shown experimentally and by computational docking. In a recent
study using single-residue mutant of humPR3 with Arg at position 217 (PR3I217R) we showed that
Ile217 located in the neighborhood of the S4 subsite pocket significantly affects the substrate specificity
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of humPR3. The docking models performed in this study using phosphonate inhibitors indicate also
that the solvent accessible surface of the S4 subsite is limited by Trp218 and Ile217 on one side. The
latter two residues are most likely responsible for the binding preference towards aliphatic side chains at
P4 and Lys99 which is located on the opposite side of the S4 subsite determines cooperation between S2
and S4 via hydrogen bonding. Introduction of a Val and a nVal at P4 and P1 positions, respectively, in
the biotinylated humPR3 inhibitor previously reported, Bt-PYDAP(O-C6H4-4-Cl)2 (2), enhanced the
kobs/[I] value towards humPR3 by ~20-fold. This was probably because the substitution of Pro4 by Val4
improved the flexibility of the inhibitor favoring the formation of hydrogen bonds between the ε-amino
group of Lys99 and Bt-Val4 amide carbonyl oxygen as well as Asp2 carboxyl group. These hydrogen
bond interactions are in agreement with previously described cooperation observed between S2 and S4
subsites. 18
Biotin at the N-terminal of P4 residue in phosphonate inhibitors and peptidyl-pNA substrates
displays stabilizing properties. General orientation, size and hydrophobic character of humPR3 S5 pocket
that accommodates N-terminal biotin is similar to that of humNE crystallized in complex with a
phosphonate inhibitor bearing a nLeu(O-Bzl) moiety at P4 and called “exopocket”, an extension of the S4
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subsite. The docking models from this study show that the terminal cavity of the humPR3 S5 pocket
formed by Phe166, Cys168 and Arg177 accomodates the biotin heterocyclic rings while the hydrophobic
surface of Ile217 interacts with the biotin aliphatic chain. The location of the biotin rings into the S5
binding site prevents recognition of the biotinylated inhibitors by extravidin by WB under non
denaturating conditions (not shown). Only the 5-carbon aliphatic chain of biotin participates in the
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stabilization of the inhibitor within the humPR3 active site as deduced from the observation that a
phosphonate inhibitors with a same peptide sequence but bearing only a N-terminal 5-carbon aliphatic
chain enhanced the inhibition rate as well as whole biotin. 18 Analysis of the docking models suggests that
the substantial impact of N-terminal biotin binding with S5 subsite on the overall inhibitory potency might
be connected with the limited size of S4 binding site. The main contribution to the binding energy at this
position is provided by Lys99 forming the hydrogen bond with the backbone of the inhibitor and
stabilizing the biotin moiety in proper orientation. Due to the narrow character of S4 subsite and the
presence of Trp218 and Ile217 on the opposite site of Lys99 there is a strong preference for small,
hydrophobic residues at P4 position. Therefore the introduction of more sizable side chain such as
nLeu(O-Bzl) may influence proper stabilization of the compound at P4 subsite, resulting in decreased
inhibitory potency.
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One of the challenges when designing preclinical studies for PR3 is to select a relevant animal
model. We previously showed that PR3 from rodents differs from humPR3 both in terms of substrate
specificity, which preclude the use of substrate-derived phosphonate inhibitors and of subcellular
distribution since there is no constitutive expression of PR3 at the neutrophil surface of rodent neutrophils.
27, 33
We therefore used a nonhuman primate model to investigate the substrate specificity of neutrophilic
PR3 and its sensitivity to phosphonate inhibitors developed against humPR3. In view of the highly
conserved primary amino acid sequence of macPR3 implying a very similar specificity as with humPR3,
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macPR3 cleaved the humPR3 substrate at the same site
and this activity was inhibited by all
phosphonate inhibitors of humPR3 used in this study. WB analysis of the macaque neutrophil lysate using
an anti-humPR3 antibody revealed the presence of a single band of 26 kDa in the neutrophil lysate with no
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glycosylated forms. A single band of 75 kDa was revealed after the lysate was incubated with human
α1PI indicating that macPR3 had formed an irreversible complex with the serpin. In keeping with this
observation, the proteolytic activity towards the humPR3 substrate in the lysate was inhibited by α1PI and
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by the PR3-specific serpinB1(STDA/R) inhibitor
(not shown). The identification of proteolytically
active macPR3 in the neutrophil lysate was further confirmed by electrophoresis under non-
denaturing/non reducing conditions using the ABP Bt-[PEG]66-PYDAP(O-C6H6-4-Cl)2 and streptavidin-
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peroxydase staining. We found similar level of active PR3 in lysates of purified human and macaque
neutrophils by kinetics and immunobloting assays. The macaque model thus appears as relevant animal
model for in vivo studies.
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CONCLUSION
Targeting the humPR3 active site by specific inhibitors has become an evidence as soon as it has
been established that it was not a redundant protease mimicking humNE, and that its proteolytic activity
was poorly controlled by physiological inhibitors. We have optimized here the structure of peptidyl
phosphonate inhibitors by coupling molecular modeling studies with kinetic analyses, and we obtained
molecular probes to follow the fate and further investigate the function of PR3 both in vitro and in vivo.
The potency and selectivity of the inhibitors developed here let suppose that they are suitable therapeutic
tools for fighting inflammatory and/or infectious diseases where the role of humPR3 has been clearly
identified or even only suspected.
EXPERIMENTAL SECTION
Materials- humNE (EC 3.4.21.37) was obtained from Athens Research & Technology (USA). The
fluorescence resonance energy transfer (FRET) substrates ABZ-VADnVADYQ-EDDnp/ABZ-
APEEIMRRQ-EDDnp and chromogenic para-nitroanilide substrates synthesized by Genecust (Dudelange
Luxembourg). IGEPAL® CA-630 (NP40) was purchased from Sigma-Aldrich (St. Louis, MO, USA).
Synthesis of peptidyl-phosphonate inhibitors- All reagents and solvents were obtained from commercial
sources and were used without purification.
All final compounds were purified to >95% purity HPLC system (Jasco LC System, Jasco, Japan)
equipped with Supelco Wide Pore C8 column (8 x 250 mm) and ultraviolet-visible (UV-VIS, 226 nm) and
fluorescent detectors (excitation 320 nm, emission 450 nm). A linear gradient from 10 to 90% of B within
40 min was applied (A: 0.1% TFA in water; B: 80% acetonitrile in A).
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The nuclear magnetic resonance spectra (1H, 31P and 13C) were recorded on either a Bruker
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Avance DRX-300 (300.13 MHz for H NMR, 121.50 MHz for 31P NMR), a Bruker Avance 600 MHz
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(600.58 MHz for H NMR, 243.10 MHz for 31P NMR, and 101.12 MHz for 13C NMR) or Bruker
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AVANCE III 700 MHz (700.67 MHz for 1H NMR) spectrometer. Chemical shifts are reported in parts per
million (ppm) relative to a tetramethylsilane internal standard. Mass spectra were recorded using a Biflex
III MALDI TOF mass spectrometer (Bruker, Germany). The cyano-4-hydroxycinnamic acid (CCA) was
used as a matrix. High resolution mass spectra (HRMS) were acquired either on a Waters Acquity Ultra
Performance LC, LCT Premier XE or Bruker micrOTOF-Q II mass spectrometer.
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Cbz-Protected 1-Aminoalkylphosphonate Diaryl Esters (General Procedure). The first step in the
synthesis of the phosphonic analogues of Ala, nVal and Abu was the preparation of tri(4-
chlorophenyl)phosphite from 4-chlorophenol and phosphorus trichloride. 36 Briefly, phosphorus trichloride
(10 mmol) was added to 4-chlorophenol (30 mmol) dissolved in acetonitrile (50 mL) and the mixture
refluxed for 6 h. The volatile elements were removed in a vacuum and the resulting crude phosphite, a
yellow oil, was used directly in an amidoalkylation reaction. It was mixed with benzyl carbamate (12
mmol) and an appropriate aldehyde: acetaldehyde, butyraldehyde or propionaldehyde (12 mmol) and
refluxed in acetic acid for 3 h (Oleksyszyn’s method 37).
Deprotection of Cbz Group (General Procedure). The Cbz protecting group was removed by incubation
with 33% hydrobromic acid in acetic acid (2 h). The volatile components were removed under reduced
pressure and the products were crystallized from methanol/diethyl ether to give target compounds as
hydrobromide salts.
Benzyl (1-(bis(4-chlorophenoxy)phosphoryl)ethyl)carbamate (12, Cbz-AlaP(O-C6H4-4-Cl)2). 12 was
prepared using the general method described above and crystallized form methanol to yield a white solid
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(56%). H NMR (300.13 MHz, CDCl3-d1, ppm): δ 7.43-6.97 (m, 14H), 5.22-5.08 (m, 2H), 4.74-4.37 (m,
1H), 1.56 (dd, J = 18.2, 7.4 Hz, 3H); 31P NMR (121.50 MHz, CDCl3-d1, ppm): δ 19.56 (s); 13C NMR
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(101.12 MHz, DMSO-d6, ppm): δ 156.16, 156.11, 151.14, 151.05, 150.84, 150.74, 137.20, 134.14,
131.91, 131.88, 128.87, 128.46, 128.34, 126.15, 126.03, 121.13, 121.09, 120.99, 119.99, 119.73, 66.48,
45.30, 43.73, 15.52. HRMS: calcd for (C22H20Cl2NO5P)H+, 480.0534; found, 480.0533.
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Benzyl (1-(bis(4-chlorophenoxy)phosphoryl)propyl)carbamate (13, Cbz-AbuP(O-C6H4-4-Cl)2). 13 was
prepared using the general method described above and crystallized form methanol to yield a white solid
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white solid (19%). H NMR (300.13 MHz, CDCl3-d1, ppm): δ 7.45-6.99 (m, 13H), 5.14 (d, J = 10.7 Hz,
1H), 5.24-5.06 (m, 2H), 4.50-4.33 (m, 1H), 2.20-2.03 (m, 1H), 1.87-1.64 (m, 1H), 1.11 (t, J = 7.3 Hz, 3H);
31P NMR (121.50 MHz, CDCl3-d1, ppm): δ 18.31 (s); 13C NMR (101.12 MHz, DMSO-d6, ppm): δ 156.85,
156.81, 149.45, 149.35, 149.12, 149.03, 137.34, 130.35, 130.28, 130.03, 129.86, 129.65, 128.88, 128.44,
128.32, 128.01, 122.94, 122.90, 122.67, 122.63, 117.44, 66.43, 51.27, 49.72, 22.46, 22.42, 11.16, 11.01.
HRMS: calcd for (C23H22Cl2NO5P)H+, 494.0691; found, 494.0699.
Benzyl (1-(bis(4-chlorophenoxy)phosphoryl)butyl)carbamate (14, Cbz-nValP(O-C6H4-4-Cl)2). 14 was
prepared using the general method described above and crystallized form methanol to yield a white solid
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(20%). H NMR (600.58 MHz, CDCl3-d1, ppm): δ 7.42-6.68 (m, 13H), 5.24-5.15 (m, 2H), 5.11 (d, J =
12.2 Hz, 1H), 4.57-4.44 (m, 1H), 2.07-1.95 (m, 2H), 1.67-1.39 (m, 2H), 1.02-0.93 (m, 3H); 31P NMR (243
MHz, CDCl3, ppm): δ 18.47 (s); 13C NMR (101.12 MHz, DMSO-d6, ppm): δ 156.85, 156.76, 156.71,
149.45, 149.35, 149.11, 149.02, 137.32, 130.36, 130.29, 130.05, 129.87, 129.65, 128.88, 128.45, 128.34,
122.95, 122.91, 122.67, 122.63, 117.44, 66.44, 49.23, 47.66, 30.63, 19.10, 18.95, 13.68. HRMS: calcd for
(C24H24Cl2NO5P)Na+, 530.0667; found, 530.0670.
Bis(4-chlorophenyl) (1-aminoethyl)phosphonate hydrobromide (15, HBr×H2N-AlaP(O-C6H4-4-Cl)2). 15
was prepared using the general method described above and crystallized form diethyl ether to yield a
white solid (97%). 1H NMR (300.13 MHz, DMSO-d6, ppm): δ 8.85 (s, 3H), 7.57-7.44 (m, 4H), 7.36-7.16
(m, 4H), 4.45-4.24 (m, 1H), 1.55 (dd, J = 18.3, 7.2 Hz, 3H); 31P NMR (121.50 MHz, DMSO-d6, ppm): δ
16.49 (s); 13C NMR (101.12 MHz, DMSO-d6, ppm): δ 148.63, 148.61, 148.53, 148.52, 130.57, 130.54,
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130.53, 129.62, 123.02, 122.98, 122.94, 117.45, 43.50, 41.93, 13.96, 13.93. HRMS: calcd for
(C14H14Cl2NO3P)H+, 346.0167; found, 346.0172.
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Bis(4-chlorophenyl) (1-aminopropyl)phosphonate hydrobromide (16, HBr×H2N-AbuP(O-C6H4-4-Cl)2).
16 was prepared using the general method described above and crystallized form diethyl ether to yield a
white solid (83%). 1H NMR (300.13 MHz, DMSO-d6, ppm): δ 8.87 (s, 2H), 7.67-7.13 (m, 8H), 4.21 (dt, J
= 13.6, 6.8 Hz, 1H), 2.24-1.74 (m, 2H), 1.11 (t, J = 7.4 Hz, 3H); 31P NMR (121.50 MHz, DMSO-d6, ppm):
δ 16.50 (s); 13C NMR (101.12 MHz, DMSO-d6, ppm): δ 148.56, 148.47, 130.58, 130.54, 123.05, 123.01,
122.97, 122.93, 48.80, 47.26, 22.01, 21.99, 10.81, 10.72. HRMS: calcd for (C15H16Cl2NO3P)H+ 360.0318;
found, 361.1123.
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Bis(4-chlorophenyl) (1-aminobutyl)phosphonate hydrobromide (17, HBr×H2N-nValP(O-C6H4-4-Cl)2).
17 was prepared using the general method described above and crystallized form diethyl ether to yield a
white solid (89%). 1H NMR (300.13 MHz, DMSO-d6, ppm): δ 8.88 (s, 2H), 7.49-7.27 (m, 8H), 4.25 (dt, J
= 13.9, 7.0 Hz, 1H), 2.06-1.78 (m, 2H), 1.71-1.46 (m, 2H), 0.90 (t, J = 7.3 Hz, 3H); 31P NMR (121.50
MHz, DMSO-d6, ppm): δ 16.55 (s); 13C NMR (101.12 MHz, DMSO-d6, ppm): δ 148.59, 148.58, 148.49,
148.48, 130.58, 130.53, 123.06, 123.02, 122.96, 122.92, 47.40, 45.85, 30.39, 30.36, 19.02, 18.92, 14.06.
HRMS: calcd for (C16H18Cl2NO3P)H+, 374.0474; found, 375.1931.
The peptides were synthesized manually by the solid-phase method using Fmoc chemistry. The
following amino acid derivatives were used: Fmoc-Pro, Fmoc-Val, Fmoc-Leu, Fmoc-Ile, Fmoc-nLeu,
Fmoc-nLeu(O-Bzl),Fmoc-Tyr(tBu), Fmoc-Asp(OtBu). The protected derivative of the C-terminal amino
acid residue, Fmoc-Asp(OtBu), was attached to the 2-chlorotrityl resin (substitution of Cl 1.46 mequiv/g)
(Calbiochem-Novabiochem AG, Switzerland) in the presence of an equimolar amount of
diisopropylethylamine (DIPEA) under anhydrous conditions in dichloromethane (DCM) solution. Peptide
chain was elongated in consecutive cycles of deprotection (20% piperidine in dimethylformamide
(DMF)/n-methylpyrrolidone (NMP) (1:1, v/v) with 1% Triton X-100) and coupling (DIC/HOBt
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chemistry; 3 equivalents of protected amino acid derivatives were used). A 10-fold molar excess of N-
acetylimidazole in DMF was used for acetylation of the N-terminus. Bt-[PEG]2-Pro-Tyr-Asp-AlaP(O-
C6H4-4-Cl)2 was synthesised via coupling of the Fmoc-PEG2 to the amino group of terminal Pro residue.
The N-terminal biotin group was conjugated using a 5-fold molar excess of biotin and 1,3-
diisopropylcarbidiimide (DIC) as the coupling agent in anhydrous DMSO for 6 h at 30°C. The synthesized
peptides were cleaved from the resin with TFE/hexane/acetic acid (1:6:1, v/v/v).
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Fully protected peptides were dissolved in DMF and their carboxyl groups were activated with
DIC and coupled with HBr×H2N-AlaP(O-C6H4-4-Cl)2, HBr×H2N-AbuP(O-C6H4-4-Cl)2 or HBr×H2N-
nValP(O-C6H4-4-Cl)2 in DMF in the presence of DIPEA. The mixture was stirred for 6 h and the DMF was
removed under reduced pressure. The resulting compounds were suspended in trifluoroacetic acid
(TFA)/phenol/triisopropylsilane/H2O (88:5:2:5, v/v/v/v) for 2 h to remove side chain protecting groups.
The crude peptides were purified by HPLC on a Beckman Gold System (Beckman, USA) with an
RP Kromasil-100, C8, 5 µm column (8 x 250 mm) (Knauer, Germany). The solvent systems were 0.1%
TFA (A) and 80% acetonitrile in A (B). Either isocratic conditions or a linear gradient were applied (flow
rate 3.0 mL/min, monitored at 226 nm). The purity of the synthesized peptides was verified on RP
Kromasil 100, C8, 5 µm column (4.6 x 250 mm) (Knauer, Germany). The peptides were eluted with a
linear gradient of the above solvent system (10%-90% B) for 30 min, flow rate 1 mL/min, monitored at
226 nm. HPLC retention times and 1H NMR spectra of final phosphonate peptide inhibitors are shown in
Table 5 and Supporting Information, respectively. Mass spectrometric analysis of the inhibitors (Table 5)
was done on a MALDI MS (a Biflex III MALDI-TOF spectrometer, Bruker Daltonics, Germany) using a
CCA matrix.
Enzymatic studies- Free humPR3 and humNE were titrated with α1PI. 38
kcat/Km determination: The specificity constants kcat/Km for peptidyl-pNA substrates were
determined under first-order conditions. 38 The cleavage of the substrates (1 mM final) was monitored by
measuring the absorbance of liberated pNA at 410 nm on the spectrophotometer (Versamax Microplate
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Reader, Molecular Devices, Sunnyvale, CA, USA). Measurements were carried out at 37°C in buffer 50
mM HEPES, 0.75 M NaCl, 0.05% NP40, pH 7.4. Final protease concentrations were 0.01-1 µM.
kobs/[I] determination: The inactivation of proteases by phosphonate inhibitors (substrate analog
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inhibitors) in the presence of the substrate by competition for the enzyme-binding site was measured by
the method of Tian and Tsou. 39 Product formation in the presence of an irreversible inhibitor approaches
an asymptote in this system, as described by: log([P∞]-[P])=log[P∞]-0.43A[Y]t
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•where [P∞] is the concentration of product formed at time approaching infinity, [P] is the
concentration of product at time t, [Y] is the inhibitor concentration, and A is the apparent inhibition rate
constant in the presence of the substrate. A is given by: A = k+o/(1 + K-1[S])
•where k+o is the rate constant for association of the inhibitor with the enzyme, K-1 is the inverted
Michaelis constant, and [S] the substrate concentration. The apparent inhibition rate constant A is the
slope of a plot of log([P∞]-[P]) against t, to give the second-order rate constant of inhibition k+o.
The rates of inhibition of purified humPR3, macPR3 (in purified blood neutrophil lysates) and
purified humNE were measured using FRET substrates (ABZ-VADnVADYQ-EDDnp (10 µM final) and
ABZ-APEEIMRRQ-EDDnp (10 µM final) in 50 mM HEPES, 0.75 M NaCl and 0.05% NP40, pH=7.4;
excitation wavelength: 320 nm / emission wavelength: 420 nm ; Spectramax Gemini (Molecular Devices,
Sunnyvale, CA, USA). Final protease concentrations were 1 nM.
Ki and k2 determination: We monitored the extent of protease inhibition at several time points for
a different inhibitor concentrations [I]. The observed rate constant for inhibition, kobs at each concentration
was determined from the slope of a semi-logarithmic plot of inhibition versus time. The kobs values were
re-plotted against inhibitor concentration and fitted to a hyperbolic equation, kobs = k2[I]/(Ki + [I]), to
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obtain values for Ki and k2
.
Detection of PR3 in biological fluids- CF sputa (50 µg proteins) were incubated with 11 (50 nM final) for
20 min at 37°C in PBS. The reaction was stopped by adding 1 volume of 2X SDS reducing buffer and
heating at 90°C for 5 min. The components of the mixture were separated by SDS-PAGE, 12%
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NaDodSO4-polyacrylamide gel electrophoresis under denaturing conditions. They were transferred to a
nitrocellulose (Hybond)-ECL (Enhanced Chemiluminescence) membrane at 4°C.
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Extravidin-peroxidase detection: Free sites on the membrane were blocked with 3% bovine serum
albumin (BSA) in 0.1% Tween in PBS for 90 min at room temperature (RT). Membranes were then given
two quick washes with PBS-Tween 0.1% and incubated for 2 h at RT with extravidin horseradish
peroxidase (HRP) (Sigma-Aldrich) (diluted 1/4000 in 3% BSA in PBS-Tween 0.1%). The extravidin-HRP
treated membrane was washed (3 x 10 min) with PBS-Tween 1% and then incubated with HRP substrate
for 3 min. Reactive bands were identified by chemiluminescence (ECL Kit).
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Immunodetection: Free sites on the membranes were blocked by incubation with 5% non-fat dried
milk in PBS-0.1% Tween for 90 min at RT. They were washed twice with PBS-Tween 0.1% and
incubated overnight with a rabbit primary anti-PR3 antibody (1:700, EPR6277 Abcam), followed by a
goat anti-rabbit IgG secondary antibody (1:7000, A9169 Sigma). These membranes were then washed and
processed as above.
Purification and lysis of M. fascicularis neutrophils- Female cynomolgus monkeys (Macaca
fascicularis) (approximately 3 years old and weighing 4-5 kg) were obtained from a commercial supplier.
All animal experiments and procedures were approved by the local animal experimentation ethics
committee (Comité d’éthique Val de Loire, (APAFIS#2982-20151105293399v6)). 5 mL of peripheral
blood samples were collected in lithium-heparin tubes from a femoral vein. Animals were kept under
spontaneous ventilation during anaesthesia with ketamine (10 mg/kg). The monitoring included pulse-
oximetry and heart rate recording. Intravenous access was secured with a 22G canula on the legs.
Anticoagulated whole blood was layered onto Ficoll density gradient and centrifuged. The purified
neutrophils (>98%) in suspension was treated with H2O for 30 sec to lyse red blood cells. The neutrophils
were then lysed in Hepes 50 mM, NaCl 0.15 M, NP40 0.5%, pH 7.4 and the supernatant was collected and
stored at -80°C.
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Chromatographic procedures and peptide analysis. Inhibitor 11 (75 µM final) was incubated with the
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cell free supernatants of sputa from CF patients at 37°C for 2 h in PBS. FRET substrate ABZ-
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[15]
VADnVADYQ-EDDnp
(20 µM final) was incubated with humR3 and macaque neutrophil lysate
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supernatant (10-500 nM) at 37°C in 50 mM HEPES, 0.75 M NaCl and 0.05% NP40, pH=7.4. The
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proteins were precipitated with absolute ethanol (4 volumes). The supernatant containing the peptides
were dried under vacuum and dissolved in 200 µL of 0.01% trifluoroacetic acid (v/v), then fractionated by
Agilent Technology 1200 Series HPLC system (Agilent Technology, CA, USA) on a C18 column (2.1 x
30 mm, Merck Millipore) at a flow rate of 0.3 mL/min with a linear gradient (0-90%, v/v) of acetonitrile
in 0.01% trifluoroacetic acid over 40 min. Eluted peaks were monitored at 220 nm.
Molecular modeling - Molecular docking was performed in order to explain interactions of Ac-
PYDAP(O-C6H4-4-Cl)2, (1), Bt-PYDAP(O-C6H4-4-Cl)2, (2), Bt-nLeu(O-Bzl)YDAP(O-C6H4-4-Cl)2 (8) and
Bt-VYDnVP(O-C6H4-4-Cl)2 (11) with humPR3 and macPR3. As a receptor the crystal structure of
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humPR3 (1FUJ.pdb) was selected. The same structure was used as a template for macPR3 3D model
obtained by means of automated homology modeling server - SWISS-MODEL. 41 For the docking studies
inhibitor molecules were used as a peptidyl phosphonic acids [Ac-PYDAP(OH)2, Bt-PYDAP(OH)2, Bt-
VYDnVP(OH)2, Bt-nLeu(O-Bzl)YDAP(OH)2] instead of di(chlorophenyl)-phosphonate esters, as this is
the form present in the “aged” protein-inhibitor complex. The ligand models were optimized using the
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MM2 force field (as implemented in ChemBio3D 12.0) while the atom types and protonation of all
43
structures were set using SPORES. The docking was carried out using Protein-Ligand ANT System
(PLANTS v. 1.2) with PLANTSCHEMPLP scoring function. 44-46 The protein molecules were treated as fixed
with the binding site center defined at a carbonyl oxygen of Ser214 and the binding site radius of 15 Å.
The distance constraints were set up to increase the preference of interaction between (a) inhibitor
phosphorus atom and the hydroxide oxygen of protease Ser195 (distance range was defined between 2.2-
4.0 Å), (b) the terminal carbon of Ala/nVal side chain of ligand P1 position and enzyme S1 binding pocket
set at γ-carbon of Ile190 (distance range: 5.5-6.5 Å for Ala and 2.2-5.0 Å for nVal), (c) Asp γ-carbon of
the inhibitor (P2 position) and PR3 ε-amine nitrogen of Lys99 (distance range 2.0-5.0 Å), (d) ligand P3-P4
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amide bond nitrogen and Val216 carbonyl oxygen of the receptor (distance range 2.0-5.0 Å). The lowest
energy binding poses obtained from docking simulations were then employed in quantum chemical
calculations of interaction energy between PR3 amino acid residues and Bt-Val4 fragment of inhibitor, to
explain the differences in activity of 11 towards human and macaque enzyme. humPR3 or macPR3
binding site was represented by all amino acid residues within 6 Å of inhibitor fragment considered
herein. Due to the presence of disulfide bridge in the vicinity of inhibitor molecule, covalently linked
Cys168 and Cys182 residues were included as a single monomer. Arg177 was found to be hydrogen-
bonded to Asn98 and Asn180 residues. To avoid disrupting the hydrogen bonding network, these three
residues were also considered as a monomer. The remaining fifteen PR3 residues were included
separately. The dangling bonds resulting from cutting the residues out of the protein scaffold were
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saturated with hydrogen atoms. PR3-inhibitor binding energy was calculated in a pairwise manner at the
47-49
second-order Møller-Plesset level of theory (MP2) using 6-31+G(d) basis set
and counterpoise
correction to eliminate basis set superposition error. 50 Quantum chemical calculations were performed in
Gaussian09 program. 51
AUTHOR INFORMATION
Corresponding Author:
Brice Korkmaz, Phone: (0033) 2 47 36 62 53; E-mail: brice.korkmaz@inserm.fr
AUTHORSHIP CONTRIBUTIONS
Brice Korkmaz supervised the work.
Brice Korkmaz and Adam Lesner participated in the research design. Carla Guarino, Natalia
Gruba, Renata Grzywa, Edyta Dyguda-Kazimierowicz, Yveline Hamon, Monika Legowska, Marcin
Skoreński, Sandrine Dallet-Choisy, Sylvain Marchand-Adam, and Christine Kellenberger conducted
the experiments. Brice Korkmaz, Adam Lesner, Francis Gauthier, Marcin Sienczyk and Dieter E.
Jenne performed data analyses. Brice Korkmaz wrote the manuscript. All authors contributed to the
writing and revision processes of the manuscript.
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DISCLOSURE OF CONFLICTS OF INTEREST
The authors declare no competing financial interests
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ACKNOWLEDGMENTS
This work was supported by the “Ministère de l'Enseignement Supérieur et de la Recherche”,
the “Région Centre” and the “Fonds Européen de Développement Régional” (Project INFINHI) and
“Polish Ministry of Science and Higher Education” granted to MW (project number IP2012 0596 72).
BK acknowledges the “Association Vaincre La Mucoviscidose” (AVLM) and the “Alexandre von
Humboldt Foundation”. MS and RG are grateful for support to Wroclaw University of Science and
Technology (Statute Funds 10401/0194/17). The authors thank Lise Vanderlynden (INSERM U-
1100), Heike Reimann (Comprehensive Pneumology Center, Institute of Lung Biology and Disease,
iLBD) for technical assistance.
ABBREVIATIONS
ABP, activity-based probe; α1PI, alpha-1-proteinase inhibitor; ABZ, ortho-aminobenzoic
acid; Bt, biotin; HPLC, high performance liquid chromatography; CG; cathepsin G, CF, cystic
fibrosis; EDDnp, N-(2.4-dinitrophenyl)ethylenediamine; FRET, fluorescence resonance energy
transfer; GPA, granulomatosis with polyangiitis; hum, human; NE, neutrophil elastase; NSP,
neutrophil serine protease; PBS, phosphate-buffered saline; PEG, polyethlene glycol; PMN,
polymorphonuclear neutrophil; pNA, para-nitroaniline; PR3, proteinase 3, WB, Western-blot.
ASSOCIATED CONTENT
Supporting Information.
Spectroscopic data of synthesized inhibitors. This material is available free of charge via the Internet
at http://pubs.acs.org.
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Supporting Information includes 1H NMR spectra together with SMILES for compounds 1-11 (PDF);
and docking poses for 1, 2, 8, 11 with the humPR3 and 11 with the macPR3 (PDB). Compound data
(CSV).
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Figure 1: Design, structure and mechanism of action of 1-aminoalkylphosphonate diaryl ester
inhibitors. A) General strategy of a substrate-based approach for covalent inhibitors development. B)
Development of a peptidyl-phosphonate inhibitor. C) Mechanism of serine proteases inhibition by 1-
aminoalkylphosphonate diaryl esters together with crystal structures of bovine trypsin (Protein Data
Bank (PDB) codes: 4I8G and 1MAY) and human matriptase (PDB code: 3NCL) at different stages of
aging process.
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Figure 2: Proposed putative model of 1 (A), 2 (B) and 8 (C) binding to the active site of humPR3.
The solvent-accessible surface area of the active site in humPR3 (PDB code: 1FUJ 12) was
made transparent to allow the visualization of the residues in stick representation. The single-letter
code of residues in the vicinity of the active site is indicated in black. Residues are labeled following
the numbering of chymotrypsin. The residues of the catalytic triad H57, D102 and S195 are
underlined. The carbon atoms of PR3 and the compounds are shown in white and cyan, respectively.
The oxygen, nitrogen, sulfur and phosphorus atoms are colored in red, blue, yellow and orange,
respectively.
Figure 3: Inhibition of humPR3 and stability of 11 in the cell free supernatants of sputa from CF
patients. A) Proposed putative model of 11 in humPR3 active center. B) Inhibition of PR3 in a
representative CF sputum supernatants. The volume of CF sputum was adjusted to give final
concentrations of PR3 ∼1 nM. Diluted samples were incubated with 11 (5 and 10 nM final) for 20 min
at 37°C. Inhibition was monitored by measuring the residual activity of PR3 on ABZ-VADnVADYQ-
EDDnp (20 µM). Purified PR3 (1 nM) was used as control. C) Selective labeling of PR3 activity in CF
sputum and neutrophil lysate. Samples (10 µg of total protein) were incubated for 20 min at 37°C with
11 (50 nM), and the mixtures were analyzed by WB using extravidin-peroxidase. D) HPLC profile of
the 11 after a 120 min incubation time with samples showing the stability of the inhibitor in sputa from
cystic fibrosis patients. Similar results were found in three independent experiments.
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