Cooperative α‐helix formation of β‐lactoglobulin and melittin induced by hexafluoroisopropanol
Cooperative α‐helix formation of β‐lactoglobulin and melittin induced by hexafluoroisopropanol
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DOI：
10.1002/pro.5560060218
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发表时间：
1997-02
期刊：
影响因子：
8
通讯作者：
N. Hirota;Y. Goto;K. Mizuno
中科院分区：
文献类型：
--
作者：
N. Hirota;Y. Goto;K. Mizuno
醇变性蛋白质的天然状态，也稳定α‐螺旋构象在未折叠的蛋白质和肽。在各种醇类中，三氟乙醇（TFE）和六氟异丙醇（HFIP）因其高诱发此类效应的潜力而常被使用。然而，TFE和HFIP比其他酒精更有效的原因尚不清楚。利用CD，我们研究了TFE和HFIP以及参比醇（甲醇、乙醇和异丙醇）在pH值为2时对牛β -乳球蛋白和蜂毒蜂毒蛋白构象的影响。在加入醇后，β -乳球蛋白表现出从天然状态（由β -片组成）到α -螺旋状态的转变，而蜂毒蛋白则从未折叠状态折叠到α -螺旋状态。在这两种情况下，醇的有效性顺序为：HFIP > TFE >异丙醇>乙醇>甲醇。采用双态机制分析了酒精诱导的跃迁，得到了自由能变化对酒精浓度依赖性的度量m值。m值的比较表明，TFE的高电位可以通过组成基团（即F原子和烷基）的加性贡献来解释。另一方面，HFIP的高潜力超出了加性效应的预期，这表明HFIP胶束状团簇的协同形成是重要的。
Alcohols denature the native state of proteins, and also stabilize the α‐helical conformation in unfolded proteins and peptides. Among various alcohols, trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) are often used because of their high potential to induce such effects. However, the reason why TFE and HFIP are more effective than other alcohols is unknown. Using CD, we studied the effects of TFE and HFIP as well as reference alcohols, i.e., methanol, ethanol, and isopropanol, on the conformation of bovine β‐lactoglobulin and the bee venom melittin at pH 2. Upon addition of alcohols, β‐lactoglobulin exhibited a transformation from the native state, consisting of β‐sheets, to the α‐helical state, whereas melittin folded from the unfolded state to the α‐helical state. In both cases, the order of effectiveness of alcohols was shown to be: HFIP > TFE > isopropanol > ethanol > methanol. The alcohol‐induced transitions were analyzed assuming a two‐state mechanism to obtain the m value, a measure of the dependence of the free energy change on alcohol concentration. Comparison of the m values indicates that the high potential of TFE can be explained by the additive contribution of constituent groups, i.e., F atoms and alkyl group. On the other hand, the high potential of HFIP is more than that expected from the additive effects, suggesting that the cooperative formation of micelle‐like clusters of HFIP is important.