Dzwolak Wojciech, Grudzielanek Stefan, Smirnovas Vytautas, Ravindra Revanur, Nicolini Chiara, Jansen Ralf, Loksztejn Anna, Porowski Sylwester, Winter Roland
Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland.
Biochemistry. 2005 Jun 28;44(25):8948-58. doi: 10.1021/bi050281t.
A model cosolvent, ethanol, has profound and diversified effects on the amyloidogenic self-assembly of insulin, yielding spectroscopically and morphologically distinguishable forms of beta-aggregates. The alcohol reduces hydrodynamic radii of insulin molecules, decreases enthalpic costs associated with aggregation-prone intermediate states, and accelerates the aggregation itself. Increasing the concentration of the cosolvent promotes curved, amorphous, and finally donut-shaped forms. According to FT-IR data, inter-beta-strand hydrogen bonding is stronger in fibrils formed in the presence of ethanol. Mechanisms underlying the polymorphism of insulin aggregates were investigated by spectroscopic (CD, FT-IR, and fluorescence anisotropy) and calorimetric (DSC and PPC) methods. The nonmonotonic character of the influence of ethanol on insulin aggregation suggests that both preferential exclusion (predominant at the low concentrations) and direct alcohol-protein interactions are involved. The perturbed hydration of aggregation nuclei appears to be a decisive factor in selection of a dominant mode of beta-strand alignment. It may override unfavorable structural consequences of an alternative strand-to-strand stacking, such as strained hydrogen bonding. A hypothetical mechanism of inducing different amyloid "strains" has been put forward. The cooperative character of fibril assembly creates enormous energy barriers for any interstrain transition, which renders the energy landscape comblike-shaped.
典型的助溶剂乙醇对胰岛素的淀粉样蛋白自组装具有深刻且多样的影响，产生了光谱和形态上可区分的β-聚集体形式。这种醇类物质减小了胰岛素分子的流体动力学半径，降低了与易于聚集的中间状态相关的焓变成本，并加速了聚集过程本身。增加助溶剂的浓度会促进形成弯曲的、无定形的，最终是甜甜圈形状的聚集体。根据傅里叶变换红外光谱（FT-IR）数据，在乙醇存在下形成的原纤维中，β链间的氢键更强。通过光谱学方法（圆二色性、傅里叶变换红外光谱和荧光各向异性）和量热法（差示扫描量热法和压力调制量热法）研究了胰岛素聚集体多态性的潜在机制。乙醇对胰岛素聚集影响的非单调特性表明，优先排斥作用（在低浓度时占主导）和醇与蛋白质的直接相互作用都参与其中。聚集核的水合作用受到扰动似乎是选择β链排列主导模式的决定性因素。它可能会克服替代链间堆积的不利结构后果，比如氢键紧张。已经提出了一种诱导不同淀粉样“菌株”的假设机制。原纤维组装的协同特性为任何菌株间的转变创造了巨大的能量障碍，这使得能量景观呈梳状。
