The natural silk spinning process - A nucleation-dependent aggregation mechanism?
The natural silk spinning process - A nucleation-dependent aggregation mechanism?
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DOI：
10.1046/j.0014-2956.2001.02614.x
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发表时间：
2001-12-01
期刊：
影响因子：
--
通讯作者：
Yu, TY
中科院分区：
文献类型：
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作者：
Li, GY;Zhou, P;Yu, TY
天然蚕丝的纺丝机理一直是一个悬而未决的问题。用圆二色谱(CD)研究了家蚕再生丝素水溶液中丝素蛋白从无规卷曲到β-折叠的构象转变和β-折叠聚集生长。一种依赖于成核的聚集机制，类似于在Prion蛋白、淀粉样β蛋白(Aβ)和α-突触核蛋白中发现的机制，其构象从可溶蛋白质转变为含有聚集体的神经毒性、不可溶的β片层，是丝纺过程的新建议。我们提出的证据表明，这一机制涉及两个步骤：(A)成核，这是一个限速步骤，涉及可溶无规卷曲转化为不可溶的β片层，随后是一系列热力学上不利的β片层单元的缔合，即形成核或种子；(B)一旦核形成，β片层单元的进一步生长在热力学上变得有利，导致贝塔片层聚集的快速扩展。聚集态生长遵循与无规卷曲丝素浓度相关的一级动力学过程。如果将β片状种子引入无规卷曲丝素溶液中，温度的升高会加速β片状聚集体的生长。这项工作加深了我们对活体天然蚕丝纺丝过程的理解。
The spinning mechanism of natural silk has been an open issue. In this study, both the conformation transition from random coil to beta sheet and the beta sheet aggregation growth of silk fibroin are identified in the B. mori regenerated silk fibroin aqueous solution by circular dichroism (CD) spectroscopy. A nucleation-dependent aggregation mechanism, similar to that found in prion protein, amyloid beta (A beta) protein, and alpha -synuclein protein with the conformation transition from a soluble protein to a neurotoxic, insoluble beta sheet containing aggregate, is a novel suggestion for the silk spinning process. We present evidence that two steps are involved in this mechanism: (a) nucleation, a rate-limiting step involving the conversion of the soluble random coil to insoluble beta sheet and subsequently a series of thermodynamically unfavorable association of beta sheet unit, i.e. the formation of a nucleus or seed; (b) once the nucleus forms, further growth of the beta sheet unit becomes thermodynamically favorable, resulting a rapid extension of beta sheet aggregation. The aggregation growth follows a first order kinetic process with respect to the random coil fibroin concentration. The increase of temperature accelerates the beta sheet aggregation growth if the beta sheet seed is introduced into the random coil fibroin solution. This work enhances our understanding of the natural silk spinning process in vivo.