Structural Investigation of Silk I Form Prepared from Crystalline Fraction of Silk Fibroin

用X-射线衍射法和电子衍射法研究了丝素晶体Silk I的结构。本研究采用凝乳酶透析法，将部分钼白僵菌丝素蛋白沉淀物和周期共多肽聚L-丙氨酸-甘氨酸共沉淀物进行透析，得到以下新的结果：(1)只有在pH<5.0的条件下，才能得到含有丝素I的沉淀物。(2)与已有的研究结果相比，分离后的丝素蛋白的晶胞尺寸和分子构象与模型多肽非常相似。晶胞尺寸为a=4.65，b=12.24，c=8.88a，由两条反平行排列的高分子链组成。每条链呈现2/1螺旋对称性，其中一个螺旋转角包含两个二肽单元，L-丙氨酸-甘氨酸。

The structure of the silk fibroin crystal, silk I, was studied by using X-ray and electron diffraction methods. Samples used in this investigation were prepared by dialysis of a fraction of B. moli silk fibroin precipitates by Chymotripsin and of the periodic co-polypeptide, poly(L-Ala-Gly).The following results were newly obtained from this project.(1) The precipitates with silk I form were obtained only when the solution was dialized under the condition of pH below 5.0.(2) In contrast to the studies carried out previously, the unit cell dimensions and the molecular conformation of the fractionated silk fibroin were quite similar to those of the model polypeptide. The orthorhombic unit cell with dimensions of a=4.65, b=12.24 and c=8.88A consists of two polymer chains aligned in an antiparallel fashion. Each chain exhibits a 2/1-helical symmetry, in which one helical turn contains two dipeptide units, L-Ala-Gly.