Fabiola G F, Bobde V, Damodharan L, Pattabhi V, Durani S
Department of Crystallography and Biophysics, University of Madras, Chennai, India.
J Biomol Struct Dyn. 2001 Feb;18(4):579-94. doi: 10.1080/07391102.2001.10506690.
The crystal structures of Boc-(D) Val-(D) Ala-Leu-Ala-OMe (vaLA) and Boc-Val-Ala-Leu-(D) Ala-OMe (VALa) have been determined. vaLA crystallises in space group P2(1),2(1),2(1), with a = 9.401 (4), b = 17.253 (5), c = 36.276 (9)A. V = 5,884 (3) A3, Z = 8, R = 0.086. VALa crystallises in space group P2(1) with a = 9.683 (9), b = 17.355 (7), c = 18.187 (9) A, beta = 95.84 (8) degrees , V = 3,040(4) A3, Z = 4, R = 0.125. There are two molecules in the asymmetric unit in antiparallel beta-sheet arrangement in both the structures. Several of the Calpha hydrogens are in hydrogen bonding contact with the carbonyl oxygen in the adjacent strand. An analysis of the observed conformational feature of D-chiral amino acid residues in oligopeptides, using coordinates of 123 crystal structures selected from the 1998 release of CSD has been carried out. This shows that all the residues except D-isoleucine prefer both extended and alphaL conformation though the frequence of occurence may not be equal. In addition to this, D-leucine, valine, proline and phenylalanine have assumed alphaR conformations in solid state. D-leucine has a strong preference for helical conformation in linear peptides whereas they prefer an extended conformation in cyclic peptides.
已测定了Boc-(D)Val-(D)Ala-Leu-Ala-OMe（vaLA）和Boc-Val-Ala-Leu-(D)Ala-OMe（VALa）的晶体结构。vaLA结晶于空间群P2(1)2(1)2(1)中，a = 9.401(4) Å，b = 17.253(5) Å，c = 36.276(9) Å，V = 5884(3) ų，Z = 8，R = 0.086。VALa结晶于空间群P2(1)中，a = 9.683(9) Å，b = 17.355(7) Å，c = 18.187(9) Å，β = 95.84(8)°，V = 3040(4) ų，Z = 4，R = 0.125。在这两种结构的不对称单元中均有两个分子呈反平行β-折叠排列。几个α碳原子上的氢与相邻链中的羰基氧形成氢键。利用从1998年发布的剑桥结构数据库（CSD）中选取的123个晶体结构的坐标，对寡肽中D-手性氨基酸残基的观测构象特征进行了分析。结果表明，除D-异亮氨酸外，所有残基均偏好伸展构象和αL构象，尽管出现频率可能不相等。除此之外，D-亮氨酸、缬氨酸、脯氨酸和苯丙氨酸在固态时呈αR构象。D-亮氨酸在线性肽中强烈偏好螺旋构象，而在环肽中则偏好伸展构象。
