Bagger Heidi L, Øgendal Lars H, Westh Peter
Roskilde University, Department of Science, Models and Systems, Universitetsvej 1, DK-4000 Roskilde, Denmark.
Biophys Chem. 2007 Oct;130(1-2):17-25. doi: 10.1016/j.bpc.2007.06.014. Epub 2007 Jul 7.
Thermal stress on bovine serum albumin (BSA) promotes protein aggregation through the formation of intermolecular beta-sheets. We have used light scattering and chromatography to study effects of (<1 M) Na(2)SO(4), NaSCN, sucrose, sorbitol and urea on the rate of the thermal aggregation. Both salts were strong inhibitors of BSA aggregation and they reduced both the size and number (concentration) of aggregate particles compared to non-ionic solutes (or pure buffer). Hence, the salts appear to suppress both nucleation- and growth rate. The non-electrolyte additives reduced the initial aggregation rate (compared to pure buffer), but did not significantly limit the extent of aggregation in samples quenched after 27 min. heat exposure (40-50% aggregation in all samples). The non-electrolytes did, however, modify the aggregation process as they consistently brought about smaller but more concentrated aggregates than pure buffer. The results are discussed along the lines of linkage- and transition state theories. In this framework, the rate of the aggregation process is governed by the equilibrium between a thermally denatured state (D) and the transition state D( not equal). Thus, the effect of a solute relies on its preferential interactions with respectively D and D( not equal). The current results do not show any correlation between the solutes' preferential interactions with native BSA and their effect on the rate of aggregation. This suggests that non-specific, "Hofmeister-type" interactions, which scale with the solvent accessible surface area, are of minor importance. Rather, salt induced suppression of aggregation is suggested to depend on the modulation of specific electrostatic forces in the D( not equal) state.
牛血清白蛋白（BSA）上的热应力通过分子间β-折叠的形成促进蛋白质聚集。我们使用光散射和色谱法研究了（<1 M）的Na₂SO₄、NaSCN、蔗糖、山梨醇和尿素对热聚集速率的影响。与非离子溶质（或纯缓冲液）相比，这两种盐都是BSA聚集的强抑制剂，它们减小了聚集颗粒的大小和数量（浓度）。因此，这些盐似乎同时抑制了成核速率和生长速率。非电解质添加剂降低了初始聚集速率（与纯缓冲液相比），但在27分钟热暴露后淬灭的样品中，并没有显著限制聚集程度（所有样品中聚集率为40 - 50%）。然而，非电解质确实改变了聚集过程，因为它们始终产生比纯缓冲液更小但更浓缩的聚集体。结果根据连接理论和过渡态理论进行了讨论。在此框架下，聚集过程的速率由热变性状态（D）和过渡态D（≠）之间的平衡决定。因此，溶质的作用取决于其分别与D和D（≠）的优先相互作用。目前的结果并未显示溶质与天然BSA的优先相互作用与其对聚集速率的影响之间存在任何相关性。这表明与溶剂可及表面积成比例的非特异性“霍夫迈斯特型”相互作用不太重要。相反，盐诱导的聚集抑制作用被认为取决于D（≠）状态下特定静电力的调节。
