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首页> 外文期刊>Biochemistry >Transition to a beta-sheet-rich structure in spidroin in vitro: The effects of pH and cations
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Transition to a beta-sheet-rich structure in spidroin in vitro: The effects of pH and cations

机译：体外在spidroin中过渡到富含β-sheet的结构：pH和阳离子的影响

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Unlike man-made fibers, the silks of spiders are spun from aqueous solutions and at atmospheric pressure in a process still poorly understood. The molecular mechanism of this process involves the conversion of a highly concentrated, predominantly disordered silk protein (spidroin) into beta-sheet-rich structures. To help store and transport the spidroins in solution, as well as probably control their conversion, a liquid crystalline arrangement is established in the storage region in the ampulla and persists into the duct. Although it has been Suggested that changes in the concentration of hydrogen and metal ions play a role in the formation of the solid thread, there is no reported evidence that these ions influence the secondary structure of native spidroin in solution. Here, we demonstrate that pH values between approximately 3.5 and 4.5 induce a slow change of conformation from the disordered to the beta-sheet-rich form. We also report that Al3+, K+, and Na+ ions induce similar changes in structure, while Ca2+ and Mg2+ stabilize the predominantly disorder state of the protein. Cs+ and Li+ have no apparent effect. Direct volumetric and spectrophotometric titration showed a pI of 4.22 +/- 10.33 and apparent pK values of 6.74 +/- 0.71 and 9.21 +/- 0.27, suggesting a mechanism for the effect of low pH on the protein and a rationale for the observed reduction in pH in the duct. We discuss the importance of these findings for the spinning process and the active role played by the spider to alter the kinetics of the transition.
机译：与人造纤维不同，蜘蛛丝是从水溶液中纺出的，并且在大气压下仍不清楚。该过程的分子机制涉及将高度浓缩的，主要是无序的丝蛋白（spidroin）转化为富含β-折叠的结构。为了帮助在溶液中储存和运输spidroins，并可能控制其转化，在壶腹的存储区域建立了液晶排列并持续进入管道。尽管已经提出氢和金属离子浓度的变化在实线的形成中起作用，但是没有报道表明这些离子影响溶液中天然蜘蛛蛋白的二级结构。在这里，我们证明pH值大约在3.5和4.5之间会引起构象从无序到富含β-折叠的形式的缓慢变化。我们还报告说，Al3 +，K +和Na +离子会诱导相似的结构变化，而Ca2 +和Mg2 +会稳定蛋白质的主要无序状态。 Cs +和Li +没有明显作用。直接体积和分光光度滴定法显示pI为4.22 +/- 10.33，表观pK值为6.74 +/- 0.71和9.21 +/- 0.27，表明了低pH值对蛋白质的影响机理以及观察到的还原的原理管道中的pH值。我们讨论了这些发现对纺丝过程的重要性以及蜘蛛改变过渡动力学的积极作用。

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