Colaco Martin, Park Jun, Blanch Harvey
Department of Chemical Engineering, University of California Berkeley, Berkeley, CA 94720, United States.
Biophys Chem. 2008 Aug;136(2-3):74-86. doi: 10.1016/j.bpc.2008.04.008. Epub 2008 May 1.
The aggregation of two negatively-charged polypeptides, poly-L-glutamic acid (PE) and a copolymer of poly-glutamic acid and poly-alanine (PEA), has been studied at different peptide and salt concentrations and solution pH conditions. The kinetics of aggregation were based on Thioflavin T (ThT) fluorescence measurements. The observed lag phase shortened and the aggregation was faster as the pH approached the polypeptides' isoelectric points. While the initial polypeptide structures of PE and PEA appeared identical as determined from circular dichroism spectroscopy, the final aggregate morphology differed; PE assumed large twisted lamellar structures and the PEA formed typical amyloid-like fibrils, although both contained extensive beta-sheet structure. Differences in aggregation behavior were observed for the two polypeptides as a function of salt concentration; aggregation progressed more slowly for PE and more quickly for PEA with increasing salt concentration. Several models of aggregation kinetics were fit to the data. No model yielded consistent rate constants or a critical nucleus size. A modified nucleated polymerization model was developed based on that of Powers and Powers [E.T. Powers, D.L. Powers, The kinetics of nucleated polymerizations at high concentrations: Amyloid fibril formation near and above the "supercritical concentration", Biophys. J. 91 (2006) 122-132], which incorporated the ability of oligomeric species to interact. This provided a best fit to the experimental data.
已在不同的肽浓度、盐浓度及溶液pH条件下，研究了两种带负电荷的多肽——聚-L-谷氨酸（PE）以及聚谷氨酸与聚丙氨酸的共聚物（PEA）的聚集情况。聚集动力学基于硫黄素T（ThT）荧光测量。随着pH接近多肽的等电点，观察到的延迟期缩短，聚集速度加快。虽然通过圆二色光谱法测定，PE和PEA的初始多肽结构看起来相同，但最终的聚集体形态有所不同；PE呈现出大的扭曲层状结构，而PEA形成典型的淀粉样纤维，尽管两者都含有大量的β-折叠结构。观察到这两种多肽的聚集行为随盐浓度的变化而不同；随着盐浓度增加，PE的聚集进展较慢，而PEA的聚集进展较快。几种聚集动力学模型与数据进行了拟合。没有一个模型能给出一致的速率常数或临界核尺寸。基于Powers和Powers [E.T. Powers, D.L. Powers, The kinetics of nucleated polymerizations at high concentrations: Amyloid fibril formation near and above the "supercritical concentration", Biophys. J. 91 (2006) 122 - 132] 的模型，开发了一种改进的成核聚合模型，该模型纳入了寡聚体相互作用的能力。这为实验数据提供了最佳拟合。
