ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The synthetic peptide Gly-L-Ala-L-Phe (C14H19N3O4 · 2H2O; GAF) crystallizes in the monoclinic space group P21, with a = 5.879(1), b = 7.966(1), c = 17.754(2) Å, β = 95.14(2)°, Dx = 1.321 g cm-3, and Z = 2. The crystal structure was solved by direct methods using the program SHELXS-86 and refined to an R value of 0.031 for 1425 reflections (〉 3σ). The tripeptide exists as a zwitterion in the crystal and assumes a near α-helical backbone conformation with the following torsion angles: ψ1 = -147.8°; φ2, ψ2 = -71.2°, -33.4°; φ3 ψ3 = -78.3°, -43.3°. In this structure, one water molecule bridges the COO- and NH3+ terminii to complete a turn of an α-helix and another water molecule participates in head-to-tail intermolecular hydrogen bonding, so that the end result is a column of molecules that looks like an α-helix. Thus, the two water molecules of crystallization play a major role in stabilizing the near α-helical conformation of each tripeptide molecule and in elongating the helix throughout the crystal. An analysis of all protein sequences around regions containing a GAF fragment by Chou-Fasman's secondary structure prediction method showed that those regions are likely to assume an α-helical conformation with twice the probability they are likely to adopt a β-sheet conformation. It is conceivable that a GAF fragment may be a good part of the nucleation site for forming α-helical fragments in a polypeptide, with the aqueous medium playing a crucial role in maintaining such transient species.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360280707
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