Conformation transition kinetics of Bombyx mori silk protein
Conformation transition kinetics of Bombyx mori silk protein
复制标题
家蚕丝蛋白的构象转变动力学
DOI：
10.1002/prot.21414
复制
发表时间：
2007-07-01
影响因子：
2.9
通讯作者：
Vollrath, Fritz
中科院分区：
文献类型：
--
作者：
Chen, Xin;Shao, Zhengzhong;Vollrath, Fritz
利用时间分辨傅立叶变换红外光谱（FTIR）技术研究了不同浓度乙醇处理再生桑蚕丝素蛋白膜和溶液后引起的构象转变。所得到的曲线显示了膜和丝素蛋白溶液的转变动力学受乙醇浓度的影响。此外，对于丝素蛋白溶液，蛋白质浓度也对动力学有影响。在低乙醇浓度下（例如，对于薄膜，低于40%v/v），薄膜和丝心蛋白溶液显示出一个阶段，其中P-片层以取决于乙醇浓度的速率缓慢形成。降低溶液中丝素蛋白的浓度也减缓了P-片层的形成。这些观察结果表明，该阶段代表成核步骤。在膜中乙醇浓度>4%或丝素蛋白溶液中乙醇浓度>50%时，在构象转变中未观察到这种成核相。我们的研究结果表明，乙醇诱导的丝素蛋白在膜和溶液中的构象转变是一个三相过程。第一阶段是β-片层结构的起始（成核），第二阶段是P-片层生长的快速阶段，而第三阶段代表先前形成的P-片层结构的缓慢完善。成核步骤可以非常快或相对慢，这取决于影响蛋白质链流动性和分子间氢键形成的因素。这些发现支持了以前的证据，即家蚕中的天然蚕丝纺丝是成核依赖的，并且家蚕（如蜘蛛）使用浓缩的丝蛋白溶液，并仔细控制加工环境的pH值和金属离子含量以加速成核步骤，从而产生快速的构象转变，将水溶性纺丝原液转化为坚韧的固体丝纤维。
Time-resolved FTIR analysis was used to monitor the conformation transition induced by treating regenerated Bombyx mori silk fibroin films and solutions with different concentrations of ethanol. The resulting curves showing the kinetics of the transition for both films and fibroin solutions were influenced by the ethanol concentration. In addition, for silk fibroin solutions the protein concentration also had an effect on the kinetics. At low ethanol concentrations (for example, less than 40% v/v in the case of film), films and fibroin solutions showed a phase in which P-sheets slowly formed at a rate dependent on the ethanol concentration. Reducing the concentration of the fibroin in solutions also slowed the formation of P-sheets. These observations suggest that this phase represents a nucleation step. Such a nucleation phase was not seen in the conformation transition at ethanol concentrations >4% in films or >50% in silk fibroin solutions. Our results indicate that the ethanol-induced conformation transition of silk fibroin in films and solutions is a three-phase process. The first phase is the initiation of beta-sheet structure (nucleation), the second is a fast phase of P-sheet growth while the third phase represents a slow perfection of previously formed p-sheet structure. The nucleation step can be very fast or relatively slow, depending on factors that influence protein chain mobility and intermolecular hydrogen bond formation. The findings give support to the previous evidence that natural silk spinning in silkworms is nucleation-dependent, and that silkworms (like spiders) use concentrated silk protein solutions, and careful control of the pH value and metallic ion content of the processing environment to speed up the nucleation step to produce a rapid conformation transition to convert the water soluble spinning dope to a tough solid silk fiber.