最短α-螺旋的理论研究(英文)

Theoretical Studies on Shortest α-Helix

在B3LYP/6-31+G**水平下的溶剂中优化得到4个残基长和5个残基长的α-螺旋.计算得到的骨架构象与蛋白质晶体结构的统计结果符合得很好.类似于一般的较长α-螺旋,观察到了C-端的散开.对很短的聚丙氨酸肽链,从焓上看310-螺旋明显比α-螺旋稳定,然而熵效应不利于310-螺旋结构.螺旋N2(N-端第二个残基)位上天冬氨酸侧链的加盖(Capping)效应明显使α-螺旋相对310-螺旋更加稳定.因而,在同样长度下α-螺旋比310-螺旋多的统计结果能够被理解.另外,最短的α-螺旋的C-端倾向于以β-转角结构结束.

We present the fully optimized structures of 4-residue and 5-residue α-helices at the B3LYP/6-31＋G level in solvent.The calculated backbone conformations are in good agreement with the statistical results from protein crystal structures.Similar to long regular α-helices,the fraying of the C-teriminal is observed.For short polyalanine peptide,310-helix is significantly more stable than α-helix in enthalpy.However,the 310-helix is destabilized by entropy effect.In addition,it has been found that the capping effect by an aspartic acid at N2（second residue from the N-terminal）significantly stabilizes the α-helix over the 310-helix.Thus,the statistics that there are more shortest α-helices than 310-helices of the same length can be understood.It has been also found that the C-terminal of the shortest α-helix tends to end with a β-turn structure.