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Crystal Structures of Chain-Folded Antiparallel β-Sheet Assemblies from Sequence-Designed Periodic Polypeptides

Krejchi, Mark T. and Cooper, Sharon J. and Deguchi, Yoshikuni and Atkins, Edward D. T. and Fournier, Maurille J. and Mason, Thomas L. and Tirrell, David A. (1997) Crystal Structures of Chain-Folded Antiparallel β-Sheet Assemblies from Sequence-Designed Periodic Polypeptides. Macromolecules, 30 (17). pp. 5012-5024. ISSN 0024-9297. doi:10.1021/ma9614050.

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The crystal structures and textures of a family of sequence-designed periodic polypeptides were investigated and analyzed using X-ray diffraction, vibrational spectroscopy, and cross-polarization magic angle spinning ^(13)C nuclear magnetic resonance. The repetitive amino acid sequences are described by −[(AG)_xEG]−, with integer x from 3 to 6. These macromolecules were prepared via bacterial expression of artificial genes and are monodisperse. Crystalline samples were obtained, and the interpretation of the X-ray diffraction results was aided by the generation of computer-simulated X-ray diffraction patterns. This allowed direct comparisons to be made with the observed texture-oriented X-ray diffraction photographs. All diffraction and spectroscopic evidence supports an antiparallel (ap) β-sheet structure, and all structures index on orthorhombic sublattices similar to those reported for Bombyx mori silk fibroin and poly(L-alanylglycine). The unit cell parameters for poly(AG)_3EG, for example, are a = 0.948 nm (hydrogen-bond direction), b = 1.060 nm (ap β-sheet stacking direction), and c = 0.695 nm (chain direction). Selective line broadening is observed for wide-angle diffraction signals with l ≠ 0 (for the 211 in particular) and gives an estimated crystal size of <4 nm in the chain direction. This, coupled with the appearance of a low-angle particle interference peak at 3.6 nm, indicates a crystal size over an order of magnitude less than the chain length and suggests an adjacent reentry chain-folded lamellar structure incorporating the ap β-sheet architecture. A structure with polar ap β-sheets and γ-turns, stacking with the hydrophobic methyl groups of the alanyl residues in contact, is selected by X-ray structure refinement to give the best match with the experimental data. The pattern of crystallization behavior of the poly(AG)_xEG family is consistent with the folding periodicity being in-phase with the amino acid sequence so that the glutamic acid residues are confined to the lamellar surfaces.

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Tirrell, David A.0000-0003-3175-4596
Additional Information:Copyright © 1997 American Chemical Society. Received September 23, 1996; Revised Manuscript Received May 8, 1997. Publication Date (Web): August 25, 1997. Abstract published in Advance ACS Abstracts, July 15, 1997. This investigation was supported by grants from the Polymers and Genetics Programs of the National Science Foundation (NSF), the NSF Materials Research Science and Engineering Center at the University of Massachusetts, the Engineering and Physical Sciences Research Council, and the Biotechnology and Biological Sciences Council (Bristol University Molecular Recognition Center). We thank Joseph Cappello of Protein Polymer Technologies, Inc., for a gift of one of the plasmids used in cloning and expression, and for helpful discussions of methods of gene design and construction. NMR spectra were acquired with the assistance of L. K. Thompson.
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Engineering and Physical Sciences Research Council (EPSRC)UNSPECIFIED
Biotechnology and Biological Sciences Research Council (BBSRC)UNSPECIFIED
Issue or Number:17
Record Number:CaltechAUTHORS:KREm1997
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Official Citation:Crystal Structures of Chain-Folded Antiparallel β-Sheet Assemblies from Sequence-Designed Periodic Polypeptides Mark T. Krejchi, Sharon J. Cooper, Yoshikuni Deguchi, Edward D. T. Atkins, Maurille J. Fournier,Thomas L. Mason, and David A. Tirrell Macromolecules 1997 30 (17), 5012-5024
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ID Code:53441
Deposited By: Anne Hormann
Deposited On:30 Jan 2015 00:06
Last Modified:10 Nov 2021 20:02

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