珍珠项链样局部有序驱动多肽折叠
Pearl-Necklace-Like Local Ordering Drives Polypeptide Collapse
摘要：
多肽骨架的折叠是蛋白质折叠的组成部分。以多聚甘氨酸为探针，研究了蛋白质在水溶液中的非平衡折叠途径。我们发现，崩溃取决于水合作用和肽内相互作用之间的竞争。一旦肽内范德华相互作用占主导地位，链沿着非平衡途径崩溃，其特征在于形成珍珠项链样的局部簇作为中间体，最终凝结成单个小球。通过将接触概率描述为沿链的距离的函数来描述这种粗化，我们提取了以线性方式增长的时间依赖性长度尺度。崩塌动力学的特征在于动态临界指数$z=0.5$，该指数远小于非生物聚合物的$z=1-2$值。这种指数的差异是由瞬时形成的链内氢键和局部排序，可能与所观察到的快速折叠时间在蛋白质中的解释。
英文摘要：
Collapse of the polypeptide backbone is an integral part of protein folding. Using polyglycine as a probe, we explore the nonequilibrium pathways of protein collapse in water. We find that the collapse depends on the competition between hydration effects and intra-peptide interactions. Once intra-peptide van der Waal interactions dominate, the chain collapses along a nonequilibrium pathway characterized by formation of pearl-necklace-like local clusters as intermediates that eventually coagulate into a single globule. By describing this coarsening through the contact probability as a function of distance along the chain, we extract a time-dependent length scale that grows in linear fashion. The collapse dynamics is characterized by a dynamical critical exponent $z=0.5$ that is much smaller than the values of $z=1-2$ reported for non-biological polymers. This difference in the exponents is explained by the instantaneous formation of intra-chain hydrogen bonds and local ordering that may be correlated with the observed fast folding times in proteins.
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