Ciajolo M R, Tuzi A, Pratesi C R, Fissi A, Pieroni O
Dipartimento di Chimica, Università di Napoli.
Biopolymers. 1990;30(9-10):911-20. doi: 10.1002/bip.360300906.
The crystal and molecular structure of the pentapeptide Boc-D-Ala-delta Phe-Gly-delta Phe-D-Ala-OMe, containing two dehydrophenylalanine residues, was determined by x-ray diffraction. The molecule crystallizes in the orthorombic P2(1)2(1)2(1) space group, with a = 10.439(3), b = 15.319(3) and c = 21.099(4) A. In the solid state, the conformation of the pentapeptide is characterized by the presence of two type III' beta-turns. Thus the peptide assumes a left-handed 3(10-helical conformation, the left sense being due to the D configuration of the alanine residues. The two unsaturated residues are located in the (i + 1) position of the first beta-turn and in the (i + 2) position of the second beta-turn, respectively. In the crystal, the helical molecules are linked head to tail by hydrogen bonds. Lateral hydrogen bonds are also formed between molecules related by a twofold screw symmetry. This gives rise to a typical mode of packing characterized by infinite helical "chains,' similar to the packing found in other oligopeptides that adopt a 3(10)-helical structure.
通过X射线衍射确定了含有两个脱氢苯丙氨酸残基的五肽Boc-D-Ala-δPhe-Gly-δPhe-D-Ala-OMe的晶体和分子结构。该分子以正交晶系P2(1)2(1)2(1)空间群结晶，a = 10.439(3)，b = 15.319(3)，c = 21.099(4) Å。在固态下，五肽的构象特征是存在两个III'型β-转角。因此，该肽呈现左手3(10)-螺旋构象，左旋是由于丙氨酸残基的D构型。两个不饱和残基分别位于第一个β-转角的(i + 1)位置和第二个β-转角的(i + 2)位置。在晶体中，螺旋分子通过氢键头对头连接。通过二重螺旋对称相关的分子之间也形成横向氢键。这产生了一种典型的堆积模式，其特征是无限螺旋“链”，类似于在其他采用3(10)-螺旋结构的寡肽中发现的堆积。
