Dzwolak Wojciech, Loksztejn Anna, Galinska-Rakoczy Agnieszka, Adachi Rumi, Goto Yuji, Rupnicki Leszek
Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland.
J Am Chem Soc. 2007 Jun 20;129(24):7517-22. doi: 10.1021/ja066703j. Epub 2007 May 23.
Unlike folding, protein aggregation is a multipathway, kinetically controlled process yielding different conformations of fibrils. The dynamics and determinism/indeterminism boundaries of misfolded conformations remain obscure. Here we show that, upon vortexing, insulin forms two distinct types of fibrils with opposite local chiral preferences, which manifest in the opposite twists of bound dye, thioflavin T. Occurrence of either type of fibrils in a test tube is only stochastically determined. By acting through an autocatalytic, "chiral amplification"-like mechanism, a random conformational fluctuation triggers conversion of the macroscopic amount of insulin into aggregates with uniformly biased chiral moieties, which bind and twist likewise the achiral dye. Although a convection-driven chiral amplification in achiral systems, which results in randomly distributed excesses of optically active forms, is known, observation of such a phenomenon in misfolded protein built of l-amino acids is unprecedented. The two optical variants of insulin fibrils show distinct morphologies and can propagate their chiral biases upon seeding to nonagitated insulin solutions. Our findings point to a new aspect of topological complexity of protein fibrils: a chiral feature of hierarchically assembled polypeptides, which is partly emancipated from the innate left-handedness of amino acids. Because altering chirality of a molecule changes dramatically its biological activity, the finding may have important ramifications in the context of the structural basis of "amyloid strains".
与折叠不同，蛋白质聚集是一个多途径的、动力学控制的过程，会产生不同构象的纤维。错误折叠构象的动力学以及确定性/不确定性边界仍不清楚。在这里，我们表明，在涡旋时，胰岛素会形成两种具有相反局部手性偏好的不同类型纤维，这表现为结合染料硫黄素T的相反扭曲。在试管中任何一种类型纤维的出现只是随机决定的。通过一种自催化的、类似“手性放大”的机制，随机的构象波动会触发宏观量的胰岛素转化为具有均匀偏向手性部分的聚集体，这些聚集体同样会结合并扭曲非手性染料。虽然已知在非手性系统中由对流驱动的手性放大，会导致光学活性形式的随机分布过量，但在由L - 氨基酸构成的错误折叠蛋白质中观察到这种现象是前所未有的。胰岛素纤维的两种光学变体显示出不同的形态，并且在接种到未搅拌的胰岛素溶液时可以传播它们的手性偏向。我们的发现指出了蛋白质纤维拓扑复杂性的一个新方面：分层组装多肽的手性特征，它部分地摆脱了氨基酸固有的左旋性。由于改变分子的手性会极大地改变其生物活性，这一发现可能在“淀粉样变毒株”的结构基础方面产生重要影响。
