Okuyama K, Somashekar R, Noguchi K, Ichimura S
Faculty of Technology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184, Japan.
Biopolymers. 2001 Oct 15;59(5):310-9. doi: 10.1002/1097-0282(20011015)59:5<310::AID-BIP1028>3.0.CO;2-5.
The molecular and crystal structure of one of the crystalline modifications of Bombyx mori, silk I, was determined by x-ray diffraction method. Cell dimensions are essentially the same as those found in the synthetic model peptide poly(L-Ala-Gly). The (straight phi, psi) values of L-Ala and Gly in the repeating unit are (-112 degrees, -6 degrees ), and (71 degrees, -99 degrees ) respectively, which are in the Bridge and the forth quadrant regions of the Ramachandran map, respectively. The observed molecular conformation in the present study has a "crank-shaft" or a S-shaped zigzag arrangement, leading to a remarkable agreement of observed and calculated structure amplitudes for both dipeptide and hexapeptide sequences, and has a reasonable hydrogen bond networks. Obtained (straight phi, psi) values are quite different from those reported by Lotz and Keith, even though overall appearances are quite similar to each other. In spite of intra- and intermolecular hydrogen-bond networks, silk I structure changes easily to the silk II by a mechanical deformation. This fragility may be due to the above peculiar crank-shaft conformation deduced from the alternating structure of alanine and glycine.
通过X射线衍射法测定了家蚕一种晶体变体——丝I的分子和晶体结构。晶胞尺寸与合成模型肽聚（L-丙氨酸-甘氨酸）中的基本相同。重复单元中L-丙氨酸和甘氨酸的（直链φ，ψ）值分别为（-112°，-6°）和（71°，-99°），分别位于拉马钱德兰图的桥形区域和第四象限区域。本研究中观察到的分子构象具有“曲轴”或S形锯齿排列，导致二肽和六肽序列的观察结构振幅与计算结构振幅显著一致，并且具有合理的氢键网络。尽管总体外观彼此非常相似，但获得的（直链φ，ψ）值与洛茨和基思报道的有很大不同。尽管存在分子内和分子间氢键网络，但丝I结构通过机械变形很容易转变为丝II。这种脆弱性可能归因于由丙氨酸和甘氨酸交替结构推导出来的上述特殊曲轴构象。
