光谱法研究pH值对再生桑蚕丝素蛋白在水溶液中结构的影响

Influence of pH Value on the Structure of Regenerated Bombyx mori Silk Fibroin in Aqueous Solution by Optical Spectroscopy

通过一系列光谱实验手段研究了再生桑蚕(Bombyxmori)丝素蛋白在水溶液中的构象转变情况.由于丝素蛋白含有较多带电荷的氨基酸残基,因此环境pH值对丝素蛋白的结构有着一定的影响:酸性越强,丝素蛋白越容易发生从无规线团到β-折叠结构转变;相对而言,碱性条件则更有利于丝素蛋白以无规线团结构稳定存在.特别是当pH在4附近时,丝素蛋白的无规结构最易发生改变;而pH为6左右时,丝素蛋白的结构则较为稳定.这种变化趋势与沿着成熟蚕腺体中丝素蛋白所处的环境及其状态相当吻合,由此表明pH值的调节是蚕在生物体中控制其丝素蛋白状态的一个相当重要的手段.这一结果对人工纺制动物丝条件的调控有着极其重要的现实意义.同时我们还发现,在相当宽的pH范围内,丝素蛋白的二级结构存在着中间体形态,表明丝素蛋白的变性过程不符合简单的二态机制.

A wonderful process of soluble silk fibroin transiting to solid silk catches great attentions for decades. In this paper, fluorescence and circular dichroism （CD） spectroscopy were used to monitor the conformational transition of regenerated Bombyx mori silk fibroin （RSF） in aqueous solutions under different pH values. It is shown that the secondary structure of RSF is very sensitive to pH value of solution. During acid driving conformational transition process, the silk protein aggregated near the isoelectric point of RSF （pi=4.22）, whereas its conformation is relatively stable as pH value is around 6. These changes are in accordance with the states and environments of fibroin along the silkworm silk gland, showing the essential way for silkworm controlling the state of fibroin by pH. On the other hand, the existence of intermediate during pH induced unfolding process implied that the conformational transition of RSF does not fit the simple two-state mechanism.