An amyloid-like fibril-forming supramolecular cross-β-structure of a model peptide: A crystallographic insight

Article abstract of DOI:10.1039/c0ob01033b

The peptide Boc-Val-Phe-OMe 1 bearing sequence similarity with the central hydrophobic cluster (CHC) of Alzheimer's Aβ^18-19 peptide self-assembles to produce amyloid-like straight unbranched fibrils as examined by atomic force microscopy and Congo red assay. Single crystal X-ray diffraction offers the atomic level structure of the supramolecular parallel β-sheet aggregation and antiparallel separation between layers (cross-β-structure).

Full text of DOI:10.1039/c0ob01033b

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Organic &
Biomolecular
Chemistry
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Cite this: Org. Biomol. Chem., 2011, 9, 3787
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PAPER
An amyloid-like fibril-forming supramolecular cross-b-structure of a model
peptide: a crystallographic insight†
Sibaprasad Maity, Pankaj Kumar and Debasish Haldar*
Received 16th November 2010, Accepted 18th February 2011
DOI: 10.1039/c0ob01033b
The peptide Boc-Val-Phe-OMe 1 bearing sequence similarity with the central hydrophobic cluster
1
8-19
(CHC) of Alzheimer’s Ab
peptide self-assembles to produce amyloid-like straight unbranched fibrils
as examined by atomic force microscopy and Congo red assay. Single crystal X-ray diffraction offers the
atomic level structure of the supramolecular parallel b-sheet aggregation and antiparallel separation
between layers (cross-b-structure).
Introduction
The conversion of a normally soluble protein into fibrillar
aggregates is the key to a range of diseases including Alzheimer’s
1
2
3
disease, Huntington’s disease, type II diabetes and prion-
4
related encephalopathies. Irrespective of sequences, a number
of proteins have a tendency to be misfolded and self-assembled
to form elongated, unbranched fibers that must be deposited
extracellularly and must share a common set of structural and
Fig. 1 (a) Parallel b-sheet, (b) antiparallel b-sheet and (c) cross-b-sheet
model of amyloid b peptide.
5
biophysical properties, which define them as amyloid. In addition,
there are number of examples of amyloid material like Lewy bodies
4
0–42
and coworkers have reported the crystal structure of Ab
and
Tycko and coworkers have used C solid state NMR
spectroscopy to determine the antiparallel b-sheet arrangement in
6
(
a-synuclein) and neurofibrillary tangles (tau-protein) that are
9
–11 15
13
Ab
.
7
deposited intracellularly. Moreover these extracellular amyloid
plaques are toxic and pathogenic. For Alzheimer’s disease, the
8
1
6–22
16
Ab
model peptide.
Ab peptides sequences are obtained from amyloid b precursor
Recent studies have established that amyloid fibrils formed from
9
1–42
protein (APP) in normal metabolism. The Ab has three specific
1
1–25
the residue Ab
at different pHs also exhibit the antiparallel
b-sheet structure. In addition, there are multiple instances of
amyloid models based on a parallel arrangement of b-sheets
Fig. 1).
Previously, we have reported the formation of amyloid-like fib-
rils from L-Ala-modified analogues of amyloid b-peptide residue
7–20, that has been adopted from the b-sheet region of non-
regions: (a) residues 1–16 at hydrophilic N-terminus, (b) residues
17
1
4
7–21, the central hydrophobic cluster (CHC) and (c) residues 29–
2 at hydrophobic C-terminus. The resultant peptide fragments
10
18
(
self-associate through strong intermolecular interactions to from
amyloid fibrils, which may be the direct or indirect cause of the
11
pathological conditions. Although there is a large body of data
on the conformation and b-sheet packing of amyloid fibrils, little
is known about the basic building blocks and aggregation process
1
19
amyloidogenic proteins. We also have discussed the intrinsic amy-
loidogenic behavior of terminally protected Alzheimer’s Ab
1
7–21
12
at atomic level.
20
peptide.
Intensive investigations are going on to unravel the detailed
molecular and structural principals behind the spontaneous
Herein we present the atomic level structure of amyloid
formation. The terminally protected peptide 1, bearing se-
quence similarity with the central hydrophobic cluster (CHC)
of Alzheimer’s Ab , self-assembles to produce amyloid-like
straight unbranched fibrils and examine by AFM and Congo red
assay. The single crystal X-ray diffraction reveals that the peptide
13
formation of these fibrils. Lansbury et al. have reported that
3
4–42
the amyloid fibrils obtained from a self-assembling peptide Ab
1
8-19
14
form a pleated antiparallel b-sheet structure (Fig. 1). Banerjee
1
self-associates to form a supramolecular parallel b-sheet layer
Department of Chemical Sciences, Indian Institute of Science Ed-
ucation and Research
–
Kolkata, Mohanpur, Nadia, West Bengal,
structure and antiparallel separation between the layers.
7
41252, India. E-mail: deba_h76@yahoo.com, deba_h76@iiserkol.ac.in;
Fax: +913325873020; Tel: +913325873119
Electronic supplementary information (ESI) available: H NMR,
1
13
Results and discussion
†
C
NMR, HRMS spectra. CCDC reference numbers 801305. For ESI
and crystallographic data in CIF or other electronic format see DOI:
The peptide Boc-Val-Phe-OMe 1 used in this study has been
1
8-19
1
0.1039/c0ob01033b
adopted from the central hydrophobic cluster (CHC) Ab
of
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Org. Biomol. Chem., 2011, 9, 3787–3791 | 3787

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the amyloid b-peptide, which is critical for fibril formation in
21
Alzheimer’s disease. The aggregation behavior of the terminally
protected peptide 1 was observed by atomic force microscope and
DLS. DLS is a rapid screening method to define nanostructures by
the presence of discrete peak intensity. From the DLS study, it was
found that peptide 1 self-assembled in freshly prepared methanol
solution into particles with an average diameter of 55 nm at a
peptide concentration of 1 mM (Fig. 2).
Fig. 4 Congo red assay of peptide 1 fibrillar aggregates showing
green-gold birefringence.
Fig. 2 DLS study of peptide 1 at 1 mM concentration showing particles
with an average diameter of 55 nm.
bound fibrils of peptide 1 under cross polarizer. These results are
consistent with Congo red binding to an amyloid b-sheet fibrillar
framework with hydrogen bridges and hydrophobic exterior.
A solution of the corresponding peptide in methanol–water
2 : 1) was incubated at 30 C over 7 days and a small amount of
◦
24
(
Solid-state FTIR spectroscopy was performed to study the
that solution was drop cast on a clean microscopic cover slip and
allowed to dry under vacuum at 30 C for 2 days. Examination
by atomic force microscopy revealed a fibrillar structure for the
reported peptide. AFM micrographs (Fig. 3) clearly show that the
peptide 1, that has sequence similarity with the Ab
and only differs by terminal protecting groups, exhibits fibrillar
morphology. The diameter of the non-branched fiber varied from
5
◦
secondary structure of the peptide 1 in fibrils. The region 1800–
-
1
1
500 cm is important for the stretching band of amide I
and bending peak of amide II and hydrogen-bonded urethane
2
5
-1
1
8-19
groups. Another informative frequency range is 3500–3200 cm ,
peptide
25
corresponding to the N–H stretching vibrations of the peptide.
An intense band at 3341 cm indicates the presence of strongly
hydrogen-bonded NH groups. No band has been observed at
around 3400 cm , indicating that all NH groups are involved in
intermolecular hydrogen bonding. The amide I band at 1667 cm
-
1
22
0 to 100 nm with lengths in several micrometre ranges.
-
1
26
-1
-
1
and amide II band at 1522 cm suggest that the peptide adopt
extensively hydrogen-bonded network in fibrils (Fig. 5).
27
Fig. 3 AFM image showing fibrillar aggregates of peptide 1.
Fig. 5 FTIR spectra of peptide 1 fibrillar aggregates.
The amyloid-like morphological property of the peptide fibrils
2
3
were further studied by a Congo red (CR) binding assay.
The structure and self-assembly of the peptide 1 at atomic level
28
Further, the aggregated fibrils obtained from the peptide were
stained by Congo red and were observed through cross polarizers.
Fig. 4 shows the typical green-gold birefringence of Congo red-
was further studied by single crystal X-ray diffraction. The solid
state conformation of peptide 1 shows that the peptide adopts
an extended backbone conformation (Fig. S1, ESI†). Most of
3
788 | Org. Biomol. Chem., 2011, 9, 3787–3791
This journal is © The Royal Society of Chemistry 2011

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◦
Table 1 Selected backbone torsion angles ( ) for peptide 1
O1–C3–N2–C4
C3–N2–C4–C5
N2–C4–C5–N1
174.9 w1
-93.2 f1
-136.1 y1
C4–C5–N1–C6
C5–N1–C6–C16
N1–C6–C16–O6
179.7 w2
-121.3 f2
29.2 y2
the backbone torsion angles (Table 1) of peptide 1 are in the b-
◦
sheet region of Ramachandran diagram [except y2 (29.2 )]. The
individual sub-units of peptide 1 are themselves regularly inter-
linked through two intermolecular hydrogen-bonding interactions
a
◦
˚
˚
N1–H1 ◊ ◊ ◊ O4 (2.18 A; 2.86 A; 135 ; a = 1 + x, y, z) and N2–
b
◦
˚
˚
H2 ◊ ◊ ◊ O3 (2.15 A; 2.99 A; 169 ; b = -1 + x, y, z) and thereby
form a supramolecular parallel b-sheet along the crystallographic
a direction (Fig. 6).
Fig. 7 Supramolecular cross-b-structure of peptide 1 at higher order
assembly along a axis.
general properties of these assemblies and validates the proposed
29
cross-b-model to define the fibril structure.
Experimental
General
All L-amino acids were purchased from Sigma chemicals. HOBt (1-
hydroxybenzotriazole) and DCC (dicyclohexylcarbodiimide) were
purchased from SRL.
Peptide synthesis
Fig. 6 Intermolecular hydrogen-bonded supramolecular parallel b-sheet
arrangement of peptide 1 along the crystallographic a direction.
The peptides were synthesized by conventional solution-phase
methods using racemization free fragment condensation strat-
egy. The Boc group was used for N-terminal protection and
the C-terminus was protected as a methyl ester. Coupling was
mediated by dicyclohexylcarbodiimide/1-hydroxyl benzotriazole
In higher order aggregation, the peptide 1 molecules organize
into a multi-layer b-sheet assembly with both the meridional 5.0
˚
˚
A and the equatorial 9.0 A distances, or reflections, observed in
29
the diffraction patterns of many amyloid fibers (Fig. 7). The first
distance is associated with the backbone separation within one
b-sheet (or layer) and the second with the backbone separation
between layers. The crystal packing is different from the G o¨ rbitz
(
DCC/HOBt). The intermediates were characterized by 500 MHz
1
13
H & CNMR and FT-IR spectoscopy. The final compound
1
13
was fully characterized by 500 MHz H NMR spectroscopy,
C
NMR spectroscopy, mass spectrometry, and IR spectroscopy. The
products were purified by column chromatography using silica
30
NH -Val-Phe-COOH hydrogen-bonded cage formation or other
2
31
self-assembled dipeptides.
(
100–200-mesh size) gel as stationary phase and n-hexane–ethyl
acetate mixture as eluent.
Conclusions
(
a) Boc-Val-OH(2). A solution of L-valine (1.17 g, 10 mmol)
In conclusion, the report presents the atomic details of the self-
assembly of peptide to form amyloid-like fibril. The peptide 1
bearing sequence similarity with the central hydrophobic cluster
in a mixture of dioxane (20 mL), water (10 mL) and 1 M NaOH
(10 mL) was stirred and cooled in an ice-water bath. Di-tert-
butylpyrocarbonate (2.4 g, 11 mmol) was added and stirring was
continued at room temperature for 6 h. Then the solution was
concentrated in vacuum to about 10–15 ml, cooled in an ice-
water bath, covered with a layer of ethyl acetate (about 50 ml)
1
8-19
(CHC) of Alzheimer’s Ab
peptide self-assembles to produce
amyloid-like straight unbranched fibrils. The X-ray crystallogra-
phy reveals that the peptide 1 forms a parallel supramolecular
b-sheet layer structure and antiparallel separation between layers
in higher order aggregation. Thus the backbone amide groups
form an extensive network of hydrogen bonds that run parallel to
the fibril long axis. The result provides important insights into the
and acidified with a dilute solution of KHSO to pH 2–3 (Congo
4
red). The aqueous phase was extracted with ethyl acetate and this
operation was done repeatedly. The ethyl acetate extracts were
pooled, washed with water and dried over anhydrous Na
2
SO
4
and
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Org. Biomol. Chem., 2011, 9, 3787–3791 | 3789

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evaporated in a vacuum. The pure material was obtained as a waxy
Dynamic light scattering
solid. Yield 2.02 g (9.30 mmol, 93.0%).
1
The particles sizes of the peptide 1 aggregates were determined by
DLS instrument (model ZETASIZER nano series nano zs) with
1 mM peptide solution in methanol.
H NMR (DMSO-d , 500 MHz, dppm, 1 mmol in 0.5 mL): 12.426
6
(
b, 1H, COOH), 6.893–6.875 (d, 1H, J = 9 Hz, NH Boc), 3.800–
a
b
3
9
1
2
1
.783 (m, 1H, C Val), 2.021–1.941 (m, 1H, C Val), 1.379 (s,
d
13
H, BOC), 0.877–0.848 (m, 6H, C Val). C NMR (DMSO-d ,
6
X-Ray crystallography
25 MHz, dppm 10 mmol in 0.5 mL): 173.51, 155.78, 77.96, 59.09,
9.52, 28.20, 19.14, 18.13, FT-IR (KBr): 3328, 2975, 2936, 1718,
Single crystal X-ray analysis of peptide 1 was recorded on a Bruker
high resolution X-ray diffractometer instruments.
-
1
508, 1396, 1369, 1255, 1163 cm . Anal. calcd for C10
H
19NO
4
(
217.26): C, 55.28; H, 8.81; N, 6.45%; Found: C, 55.31; H, 8.83;
N, 6.42%.
Morphological studies
(
b) Boc-Val-Phe-OMe (1). 2.0 g (9.20 mmol) of Boc-Val-OH
The morphology of the reported compound was investigated by
was dissolved in 25 ml dry DCM in an ice-water bath. H-Phe-OMe
was isolated from 3.957 g (18.4 mmol) of the corresponding methyl
ester hydrochloride by neutralization, subsequent extraction with
ethyl acetate and ethyl acetate extract was concentrated to 10 ml.
It was than added to the reaction mixture, followed immediately
by 1.898 g (9.20 mmol) dicyclohexylcarbodiimide (DCC) and
atomic force microscopy (AFM). A small amount of solution
-1
(
1 mg mL MeOH: H
2
O 2 : 1 v/v) of the corresponding com-
◦
pounds was incubated at 30 C over 7 days and placed on a
clean microscope cover glass and then dried by slow evaporation.
The material was then allowed to dry under vacuum at 30 C for
◦
two days. Images were taken with an NTMDT instrument, model
no. AP-0100 in semicontact-mode.
1
.408 g (9.20 mmol) of HOBt. The reaction mixture was allowed
to come to room temperature and stirred for 48 h. DCM was
evaporated and the residue was dissolved in ethyl acetate (60 ml)
and dicyclohexylurea (DCU) was filtered off. The organic layer
was washed with 2 M HCl (3 ¥ 50 ml), brine (2 ¥ 50 ml), 1 M
sodium carbonate (3 ¥ 50 ml) and brine (2 ¥ 50 ml) and dried over
anhydrous sodium sulfate; and evaporated in a vacuum to yield
Boc-Val-Phe-OMe as a white solid. The product was purified by
silica gel (100–200 mesh) using n hexane – ethyl acetate (3 : 1) as
Congo red assay
An alkaline saturated Congo red solution was prepared. The
dried peptide fibrils from methanol–water were stained by alkaline
Congo red solution (80% methanol/20% glass distilled water
containing 10 ml of 1% NaOH) for 2 min and then the excess stain
(Congo red) was removed by rinsing the stained fibril with 80%
methanol/20% glass distilled water solution for several times. The
stained fibrils were dried under vacuum at room temperature for
24 h, then visualized at 40¥ magnification and birefringence was
observed between crossed polarizers (Olympus optical microscope
equipped with polarizer and CCD camera).
eluent. Yield: 2.61 g (6.89 mmol, 74.89%).
1
H NMR (CDCl ,500 MHz, dppm 1 mmol in 0.5 mL): 7.299–
3
7
.101 (m, 5H, aromatic protons), 6.317–6.306 (d, 1H, J = 5.5 Hz,
NH Phe), 5.006–4.991 (d, 1H, J = 7.5 Hz, NH Boc), 4.888–
a
a
4
3
.849 (m, 1H, C Phe), 3.902–3.874 (m, 1H, C Val), 3.709 (s,
b
b
H, OMe), 3.159–3.086 (m, 2H,C Phe), 2.101–2.062 (m, 1H, C
d
13
Val), 1.443 (s, 9H, BOC), 0.963–0.910 (m, 6H, C Val). C NMR
125 MHz, 10 mmol in 0.5 mL CDCl ): 171.64, 171.24, 155.65,
35.64, 129.15, 128.52, 127.06, 79.71, 59.78, 53.06, 52.18, 37.89,
0.81, 28.22, 19.06. M.P: 82–83 C. Mass spectra: [M + Na ]:
01.4155. [M + K] : 416.4383. FT-IR (KBr): 3341, 2972, 2962,
Acknowledgements
(
3
1
3
4
2
We acknowledge the DST, New Delhi, India, for financial assis-
tance, Project No. (SR/FT/CS-041/2009). S. Maity acknowledge
C.S.I.R., New Delhi, India, for financial assistance.
◦
+
+
-
1
940, 1743, 1733, 1677, 1667, 1522, 1300, 1273, 1248, 1170 cm .
(378.46): C, 63.47; H, 7.99; N, 7.40%;
Anal. calcd for C20
H
30
N
2
O
5
Notes and references
Found: C, 63.48; H, 8.10; N, 7.42%.
1
P. T. Lansbury, Acc. Chem. Res., 1996, 29, 317; G. Taubes, Science,
1
1
996, 271, 1493; R. Baumeister and S. Eimer, Angew. Chem., Int. Ed.,
998, 37, 2978.
NMR experiments
2
S. Chen, F. A. Ferrone and R. Wetzel, Proc. Natl. Acad. Sci. U. S. A.,
002, 99, 11884; Y. N. Machida, M. Kurosawa, N. Nukina, K. Ito, T.
All NMR studies were carried out on a Br u¨ ker AVANCE 500 MHz
spectrometer at 278 K. Compound concentrations were in the
2
Oda and M. Tanaka, Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 9679.
L. Marzban and C. B. Verchere, Diabetes, 2004, 28, 39.
S. B. L. Ng and A. Doig, Chem. Soc. Rev., 1997, 26, 425; S. B. Prusiner,
Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 13363.
3
4
range 1–10 mmol in CDCl
3
and (CD
3
2
) SO.
FT-IR spectroscopy
5 J. C. Rochet and P. T. Lansbury, Curr. Opin. Struct. Biol., 2000, 10, 60.
6
7
8
M. Sadqi, F. Hern a´ ndez, U. Pan, M. P e´ rez, M. D. Schaeberle, J. Avila
and V. Mu n˜ oz, Biochemistry, 2002, 41, 7150.
All reported solid-state and fibril FT-IR spectra were obtained
with a Perkin Elmer Spectrum RX1 spectrophotometer with the
KBr disk technique.
E. Junn, R. D. Ronchetti, M. M. Quezado, S. Y. Kim and M. M.
Mouradian, Proc. Natl. Acad. Sci. U. S. A., 2003, 100, 2047.
B. Dermaut, S. K. Singh, C. D. Jonghe, M. A. Cruts, U. L o¨ igren, P.
L u¨ bke, R. Cras, P. P. Dom, D. Deyn, J. J. Martin and C. V. Broeckhoven,
Brain, 2001, 124, 2383.
Mass spectrometry
9
L. Puglielli, R. E. Tanzi and D. M. Kovacs, Nat. Neurosci., 2003, 6,
3
45.
Mass spectra were recorded on a Q-Tof Micro YA263 high-
resolution (Waters Corporation) mass spectrometer by positive-
mode electrospray ionization.
1
0 T. S. Burkoth, T. L. S. Benzinger, V. Urban, D. M. Morgan, D. M.
Gregory, P. Thiyagarajan, R. E. Botto, S. C. Meredith and D. G. Lynn,
J. Am. Chem. Soc., 2000, 122, 7883.
3
790 | Org. Biomol. Chem., 2011, 9, 3787–3791
This journal is © The Royal Society of Chemistry 2011

View Online
1
1
1 G. T. Dolphin, P. Dumy and Garcia, Angew. Chem., Int. Ed., 2006, 45,
699.
2 E. Gaggelli, H. Kozlowski, D. Valensin and G. Valensin, Chem. Rev.,
006, 106, 1995; E. E. Nesterov, J. Skoch, B. T. Hyman, W. E. Klunk,
22 J. C. Rochet and P. T. Jr. Lansbury, Curr. Opin. Struct. Biol., 2000, 10,
60.
2
23 D. L. Taylor, R. D. Allen and E. P. Benditt, J. Histochem. Cytochem.,
2
1974, 22, 1105.
B. J. Bacskai and T. M. Swager, Angew. Chem., Int. Ed., 2005, 44, 5452;
A. K. Paravastu, I. Qahwash, R. D. Leapman, S. C. Meredth and R.
Tyco, Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 7443.
24 R. Meital, Y. Parot and E. Gazit, J. Biol. Chem., 2002, 277, 35475; Y. S.
Kim, T. W. Randolph, M. C. Manning, F. J. Stevens and J. F. Carpenter,
J. Biol. Chem., 2003, 278, 10842.
25 (a) C. Toniolo and M. Palumbo, Biopolymers, 1977, 16, 219–224; (b) V.
Moretto, M. Crisma, G. M. Bonora, C. Toniolo, H. Balaram and P.
Balaram, Macromolecules, 1989, 22, 2939–2944.
26 G. P. Dado and S. H. Gellman, J. Am. Chem. Soc., 1994, 116,
1054.
1
3 M. Paz and L. Serranno, Proc. Natl. Acad. Sci. U. S. A., 2004, 101, 87;
R. Azriel and E. Gazit, J. Biol. Chem., 2001, 276, 34156; O. S. Makin,
E. Atkins, P. Sikorski, J. Johansson and L. C. Serpell, Proc. Natl. Acad.
Sci. U. S. A., 2005, 102, 315; R. P. Friedrich, K. Tepper, R. Ronicke, M.
Soom, M. Westermann, K. Reymann, C. Kaether and M. Fandrich,
Proc. Natl. Acad. Sci. U. S. A., 2010, 107, 1942; M. R. Sawaya, S.
Sambashivan, R. Nelson, M. I. Ivanova, S. A. Sievers, M. I. Apostol,
M. J. Thompson, M. Balbirnie, J. J. W. Wiltzius, H. T. McFarlane, A. O.
Madsen, C. Riekel and D. Eisenberg, Nature, 2007, 447, 453; R. Nelson,
M. R. Sawaya, M. Balbirnie, A. O. Madsen, C. Riekel, R. Grothe and
D. Eisenberg, Nature, 2005, 435, 773.
27 S. E. Blondelle, B. Forood, A. R. Houghten and E. Peraz-Paya,
Biochemistry, 1997, 36, 8393; P. I. Haris and D. Chapman, Biopolymers,
1995, 37, 251.
28 Crystal data for peptide 1: C20
30 2 5
H N O , Mw = 378.46, orthorhombic,
space group P2
1
2
1
2
1
, a = 5.105(5), b = 10.205(12), c = 40.956(4) A˚ , U =
2134 A˚ , Z = 4, dm = 1.178 Mg m . Intensity data were collected with
3
-3
1
1
4 P. T. Lansbury, P. R. Costa, J. M. Griffiths, E. J. Simon, M. Auger,
K. J. Halverson, D. A. Kocisko, Z. S. Hendsch, T. T. Ashburn, R. G. S.
Spencer, B. Tidor and R. G. Griffin, Nat. Struct. Biol., 1995, 2, 990.
5 J. Naskar, M. G. B. Drew, I. Deb, S. Das and A. Banerjee, Org. Lett.,
Mo-Ka radiation at room temperature using Bruker APEX-2 CCD
diffractometer. The crystal was positioned at 70 mm from the Image
◦
Plate. 100 frames were measured at 2 intervals with a counting time
of 5 min to give 14 620 independent reflections. Data were processed
using the Bruker SAINT package and the structure solution and
2
008, 10, 2625; S. Ray, A. K. Das, M. G. B. Drew and A. Banerjee,
32
Chem. Commun., 2006, 4230.
refinement procedures were performed using SHELX97. The non-
hydrogen atoms were refined with anisotropic thermal parameters. The
hydrogen atoms were included in geometric positions and given thermal
parameters equivalent to 1.2 times those of the atom to which they were
1
1
1
6 J. J. Balbach, Y. Ishii, O. N. Antzutkin, R. D. Leapman, N. W. Rizto,
F. Dyda, J. Reed and R. Tycko, Biochemistry, 2000, 39, 13748.
7 A. T. Petkova, G. Buntkowsky, F. Dyda, R. D. Leapman, W. M. Yau
and R. Tycko, J. Mol. Biol., 2004, 335, 247.
attached. The final R values were R
1
2
0.0453 and wR 0.1315 for 2070
8 A. T. Petkova, Y. Ishii, J. J. Balbach, O. N. Antzutkin, R. D. Leapman,
F. Delaglio and R. Tycko, Proc. Natl. Acad. Sci. U. S. A., 2002, 99,
data with I > 2s(I). The largest peak and hole in the final difference
Fourier were -0.15 and 0.17 e A˚ . The data have been deposited at
-3
1
6742; K. Iwata, T. Fujiwara, Y. Matsuki, H. Akutsu, T. S. H. Naiki
the Cambridge Crystallographic Data Center with reference number
CCDC 801305.
and Y. Goto, Proc. Natl. Acad. Sci. U. S. A., 2006, 103, 18119; S. A.
Jayasinghe and R. Langen, J. Biol. Chem., 2004, 279, 48420; A. Der-
Sarkissian, C. C. Jao, J. Chen and R. Langen, J. Biol. Chem., 2003, 278,
29 K. Channona and C. E. MacPhee, Soft Matter, 2008, 4, 647.
30 C. H. Gorbitz, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58, 512.
31 (a) P. Tamamis, L. A. Abramovich, M. Reches, K. Marshall, P. Sikorski,
L. Serpell, E. Gazit and G. Archontis, Biophys. J., 2009, 96, 5020;
(b) A. M. Smith, R. J. Williams, C. Tang, P. Coppo, R. F. Collins, M. L.
Turner, A. Saiani and R. V. Ulijn, Adv. Mater., 2008, 20, 37; (c) L. Chen,
K. Morris, A. Laybourn, D. Elias, M. R. Hicks, A. Rodger, L. Serpell
and D. J. Adams, Langmuir, 2010, 26, 5232.
3
7530.
1
2
2
9 D. Haldar and A. Banerjee, Int. J. Pept. Res. Ther., 2006, 12, 341.
0 D. Haldar and A. Banerjee, Int. J. Pept. Res. Ther., 2007, 13, 439.
1 D. M. Walsh, D. M. Hartley, M. M. Condron, D. J. Selkoe and D. B.
Teplow, Biochem. J., 2001, 355, 869; B. Urbanc, L. Cruz, S. Yun, S. V.
Buldyrev, G. Bitan, D. B. Teplow and H. E. Stanley, Proc. Natl. Acad.
Sci. U. S. A., 2004, 101, 17345.
32 G. M. Sheldrick, SHELX97, University of G o¨ ttingen, Germany, 1997.
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