Asakura Tetsuo, Nakazawa Yasumoto
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
Macromol Biosci. 2004 Mar 15;4(3):175-85. doi: 10.1002/mabi.200300098.
The structure of silk fibroin from a wild silkworm, S. c. ricini, the amino acid sequence of which consists of repeated poly-Ala and Gly-rich regions, was examined by using solution and solid-state NMR methods. The structural transition of the silk fibroin in aqueous solution was monitored by using 13C solution NMR spectroscopy as a function of temperature. The fast exchange with respect to the chemical shift between the helix and coil conformations was observed in the poly-Ala region and the slow conformational change from alpha-helix to random coil was observed for the Gly residue adjacent to the N-terminal Ala residue of the poly-Ala region. The torsion angles of several Ala and Gly residues in the model peptide, GGAGGGYGGDGG(A)12GGA-GDGYGAG, were determined by the conformation-dependent 13C chemical shifts, rotational echo double resonance (REDOR) and 2D spin-diffusion NMR methods. The solid-state NMR analysis leads to the precise silk structure before spinning, where the poly-Ala sequence takes a typical alpha-helix pattern with a tightly winded helical structure at both terminal regions of the poly-Ala sequence. This is expected to stabilize the alpha-helical structure of the poly-Ala region in S. c. ricini silk fibroin from the silkworm.
对一种野生蚕蓖麻蚕（Samia cynthia ricini）的丝素蛋白结构进行了研究，其氨基酸序列由重复的聚丙氨酸和富含甘氨酸的区域组成，采用了溶液和固态核磁共振方法。通过使用13C溶液核磁共振光谱作为温度的函数，监测了丝素蛋白在水溶液中的结构转变。在聚丙氨酸区域观察到螺旋和线圈构象之间相对于化学位移的快速交换，并且在聚丙氨酸区域N端丙氨酸残基相邻的甘氨酸残基处观察到从α-螺旋到无规卷曲的缓慢构象变化。通过构象依赖性13C化学位移、旋转回波双共振（REDOR）和二维自旋扩散核磁共振方法确定了模型肽GGAGGGYGGDGG(A)12GGA-GDGYGAG中几个丙氨酸和甘氨酸残基的扭转角。固态核磁共振分析得出了纺丝前精确丝结构，其中聚丙氨酸序列在聚丙氨酸序列的两个末端区域呈现典型的α-螺旋模式，具有紧密缠绕的螺旋结构。这有望稳定蓖麻蚕丝素蛋白中聚丙氨酸区域的α-螺旋结构。
