Lei Hongxing, Smith Paul E
Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506-3702, USA.
Biophys J. 2003 Dec;85(6):3513-20. doi: 10.1016/S0006-3495(03)74771-7.
The effects of a T3S mutation on the stability of a 3:5 beta-hairpin forming peptide (YITNSNGTWT) are investigated. Molecular dynamics simulations in explicit water indicate that the wild-type peptide forms a stable hairpin whereas the T3S mutant does not, in agreement with the experimental data. Thermodynamic integration calculations for the mutation of Thr to Ser suggest that the free-energy changes in the folded state are small, but the corresponding changes in the unfolded state are large and favorable. One of the main reasons for the difference appears to be the formation of a stable cluster involving the Tyr1 and Ser3 hydroxyl groups and their interaction with the C-terminal carboxylate group, which was observed after unfolding of the T3S mutant. Further analysis of the side-chain preferences of Thr and Ser indicate that the corresponding cluster in the wild-type peptide is unstable due to the high preference of the Thr chi1 dihedral for g+ states, which appeared to be incompatible with formation of a stable cluster. The results suggest that one should consider the nature of the unfolded state when attempting to fully explain the effects of mutations on hairpin stability.
研究了Ⅲ型分泌系统（T3S）突变对形成3:5β-发夹结构肽（YITNSNGTWT）稳定性的影响。在明确的水环境中的分子动力学模拟表明，野生型肽形成了稳定的发夹结构，而T3S突变体则没有，这与实验数据一致。苏氨酸（Thr）突变为丝氨酸（Ser）的热力学积分计算表明，折叠态的自由能变化很小，但未折叠态的相应变化很大且是有利的。这种差异的主要原因之一似乎是在T3S突变体展开后观察到的，涉及Tyr1和Ser3羟基及其与C端羧基相互作用的稳定簇的形成。对Thr和Ser侧链偏好的进一步分析表明，野生型肽中的相应簇是不稳定的，这是由于Thr的χ1二面角对g+状态的高度偏好，这似乎与稳定簇的形成不相容。结果表明，在试图全面解释突变对发夹稳定性的影响时，应该考虑未折叠态的性质。
