J. Brabcová et al. / Journal of Molecular Catalysis B: Enzymatic 98 (2013) 62–72
65
instruments were controlled with the software packages HyStar
3.2 and micrOTOF-control 3.0. The data were collected and manip-
ulated with the software packages ProteinScape 3.0, DataAnalysis
4.0, and BioTools 3.2 (Bruker Daltonics).
The peptide mixture (5 L) was injected into a NS-AC-11-
C18 Biosphere C18 column (particle size: 5 m, pore size: 12 nm,
length: 150 mm, inner diameter: 75 m), with a NS-MP-10 Bio-
sphere C18 pre-column (particle size: 5 m, pore size: 12 nm,
length: 20 mm, inner diameter: 100 m), both manufactured by
NanoSeparations (Nieuwkoop).
The separation of peptides was achieved via a linear gradient
between mobile phase A (water) and B (acetonitrile), both contain-
ing 0.1% (v/v) formic acid. A four step linear gradient of 5–30% in
70 min, 30–50% in 10 min, 50–100% in 8 min and 100% B for 2 min
was used (the flow rate was 250 L/min at 25 ◦C).
methanol/water (4:1, v/v) as the mobile phase at 0.3 mL/min. The
eluate was monitored at 220, 254 and 275 nm while the UV spectra
were run from 200 to 300 nm.
The products of hydrolysis of peracetylated thymidine were
analyzed by HPLC (column Kromasil C18, the flow 1 mL/min, UV
detection at 260 nm). The mobile phase was composed of medium
A: 10 mM ammonium dihydrogen phosphate (pH 4.2, 90%): ace-
tonitrile (10%) and medium B: acetonitrile (90%): distilled water
(10%) under conditions of the analysis: 0–6 min 100% A, 6–14 min
65% A and 35% B, 14–18 min 100% A. The retention times were: per-
acetylated thymidine – 2.1 min, monodeprotected 3ꢀOH – 7.6 min,
monodeprotected 5ꢀOH – 8.4 min, acetylated thymidine – 13.3 min.
2.12. Calculation of enantiomeric excess and E value
Mass spectra processing: Data were processed using Protein-
Scape and BioTools software. Trypsin was chosen as the enzyme
parameter. One missed cleavage was allowed, and an initial pep-
tide mass tolerance of 15.0 ppm was used for MS and 0.03 Da for
MS/MS analysis. Cysteines were assumed to be carbamidomethy-
lated, and methionine was allowed to be oxidated. All these possible
modifications were set to be variable. Monoisotopic peptide charge
was set to 1+, 2+ and 3+. Only significant hits (Mascot score ≥80),
as defined by the MASCOT probability analysis (P < 0.05) were
accepted.
For the construction of the 3D models of both lipases we
used as a template a publicly available crystal structure of the
LIP2 from G. candidum identifier 1THG from Protein Data Bank
alignment the modeled sequences of the Lip1 and Lip2 was uti-
1THG were inputs into modeling environment (MOE). The homol-
ogy module of the MOE program was used for the modeling of the
Lip1 and the Lip2 structures [38]. The final models were subject of
geometry optimization in parm99 force field to adjust local minima
geometry for given model.
To calculate the enantiomeric excess values (eep and ees), the
ratio of the corresponding enantiomers was determined by an
analysis of diastereoisomeric derivatives of the respective chiral
compounds. The synthesized convenient diastereoisomeric deriva-
tives were the diastereoisomeric esters of the chiral alcohols
with the respective pure enantiomers of (R)-(+)-3,3,3-trifluoro-2-
methoxy-2-phenylpropanoic acid (MTPA, Mosher acid). The second
method consisted of the application of a chiral stationary phase of
a cyclodextrin type to separate enantiomers of the chiral alcohols
using chiral HPLC analysis. A combination of both methods gives
two independent analytical methods for assigning the absolute
configuration of the major enantiomers of chiral alcohols [39–42].
The absolute configurations of the major enantiomers of the MTPA
esters were assigned by measuring their 1H and 19F NMR spectra.
Three key parameters allow an efficient evaluation of an enzyme-
mediated resolution process: the optical purity of the product,
expressed as enantiomeric excess of the chiral product (eep) or that
of the deracemized substrate (ees), the extent of conversion of the
racemic substrate c (c = ees/(ees + eep)), and the enantiomeric ratio
E (E = ln[1 − c(1 + eep)]/ln[1 − c(1 − eep)]).
The higher is the E value, the higher is the value of the cor-
responding enzyme-mediated process in a selection procedure
aiming to use the optimum enzymic system for the production of
a chiral compound with requested absolute configuration.
2.10. Circular dichroism and fluorescence spectroscopy
Circular dichroism spectra of the three pure lipases were
recorded in a Chirascan spectropolarimeter (Applied Photophysics)
at 25 1 ◦C. Far-UV CD spectra were measured at wavelengths
between 190 and 250 nm in a 1 mm path-length cuvette, with 2 M
protein solutions in distilled water on a Varian Cary Eclipse Fluo-
rescence Spectrophotometer (Agilent Technologies). The intrinsic
tryptophan fluorescence was monitored using an excitation wave-
length of 280 nm, with excitation and emission bandwidths of
5 nm, and recording fluorescence emission spectra between 300
and 400 nm.
3. Results and discussion
produced by G. candidum strain 4013
produced by yeast G. candidum strain 4013 showed a high num-
ber of bands (Fig. 1). Non-denaturing electrophoresis, revealed the
presence of at least three enzymes with esterase activity (Fig. 1,
Scheme 1). In order to separate pure lipases from crude mix-
ture a selective purification strategy based on domino purification
by using matrixes with different hybrophobicity was developed
(Fig. 2). The molecular mass were calculated from SDS-PAGE gels
using GelAnalyzer version 2012a – 70.5 kDa lipase for Lip1, 75.5 kDa
for Lip2 and 43 kDa for Lip3.
More than 76% of the active protein was adsorbed on the support
(octyl-Sepharose) during 17 h. Further addition of support did not
improve the immobilization yield.
The supernatant after immobilization showed hydrolytic activ-
ity toward pNPB, which confirmed the presence of lipases or
esterases. The immobilization on hydrophobic support is a method
how to selectively adsorb lipases with presence of the esterases.
However, sometimes a more hydrophobic material is needed
[10] due to various nature of lipases. Matrixes with different
hydrophobic degree (butyl-Sepharose, phenyl-Sepharose, Lewatit,
2.11. Analytical methods
Characterization of the products of biotranformations (1–6) was
performed by the 1H NMR and the 19F NMR spectra were recorded
on a Varian UNITY 500 spectrometer (in a FT mode) at 499.8
and 470.3 MHz, respectively, in deuteriochloroform using either
tetramethylsilane (ı 0.0) as the internal reference or hexafluo-
robenzene as external reference (ı – 162.9). Preparative column
chromatography was performed on a silica gel type 60 (parti-
cle size 0.04–0.063 mm). TLC was performed on aluminum sheets
precoated with silica gel 60. Analytical HPLC was carried out on
a Thermoseparation Products instrument equipped with a Con-
staMetric 4100 Bio pump and a SpectroMonitor 5000 UV DAD.
Analysis of the chiral products was performed on a chiral Nucle-
odex -OH column (150 × 4 mm; Macherey-Nagel, Germany) using