金属离子导致的丝素蛋白的构象转变

蚕丝和蜘蛛丝的优异力学性能一直是科学家们关注的课题^1-3]。近年来，在蚕丝蛋白结构及其构象方面的研究取得了许多进展^3-5]。在蚕的腺体中丝素蛋白的构象为silk I（主要是无规线团为主，还有少量的β－转角，α螺旋等），而在纤维状的丝中为silk Ⅱ（主要是β折叠）。金属离子在蚕叶丝过程中的作用也一直是一个人们关心的问题。Chen等^6]在研究丝胶（包附在丝素蛋白表层的另外一种蛋白）时发现，在一定pH条件下，Ni^2 离子通过四配位的螯合作用诱导丝素蛋白β折叠的形成。并且，Viney等^7]根据电感耦合等离子体（ICP－MS）技术推测Ca^2 的增加能使β折叠的形成加速。

The Effect of Metal Ions on the Conformation Transition of Silk Fibroin

How the silkworm spins out such an excellent silk fiber has been a hot topic. The issue here is to know how the coil chains in the gland of silkworm transform to β-sheet in silk fiber. We used the regenerated silk fibroin to imitate the silk fibroin of the gland to investigate the effect of metal ion(Ca2+. Cu2+) on the silk spinning process of Bombyx mori silkworm. The solutions or gel obtained from hte mixture of regenerated silk fibroin and metal ions were dried for mimicking the gradual loss of water in the spinning process. The 13C NMR spectrum simulation for Cβ nucleus of alanine quantitatively demonstrated that the conformation of the regenerated silk fibroin is dominantly of silk Ⅰ, whereas the fibroin with metal ions has more silk Ⅱ conformation. Raman spectroscopies show the consistent results with that of NMR. The binding of metal ion with carbonyl and amide in protein backbone allows the protein chain to array regularly, therefore leading to the β-sheet formation.