The intrinsic helix-forming tendency of L-alanine.
The intrinsic helix-forming tendency of L-alanine.
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DOI：
10.1073/pnas.89.16.7821
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发表时间：
1992-08
影响因子：
11.1
通讯作者：
J. Vila;Roger Williams;J. A. Grant;J. Wójcik;H. Scheraga
中科院分区：
文献类型：
--
作者：
J. Vila;Roger Williams;J. A. Grant;J. Wójcik;H. Scheraga
已对三种十六肽在水中进行了构象能计算-即，具有序列乙酰基-AAAAAAAAAA-KAAAAKA-酰胺的共聚物，3 K（I），以带电和中性形式;具有序列乙酰基-AAQAAAAQAAAAQAAY-酰胺的中性肽，AQY;和具有乙酰基和酰胺端基的16-残基L-丙氨酸均聚物。构象能是肽的经验构象能程序（ECEPP/2）势能加上连续水化自由能的总和。一个经验（JRF）参数集被用于水合自由能，连同静电贡献的溶剂效应带电赖氨酸。计算出的带电3 K（I）的最可几构象的相对高的螺旋含量和AQY的中间螺旋含量与实验值相当吻合。计算出的丙氨酸均聚物的螺旋含量非常低，这与嵌段共聚物和主客体无规共聚物的实验结果一致。计算表明，计算的3 K（I）的高螺旋含量是由于赖氨酸残基的内能和水合自由能的总和，而不是丙氨酸的高内在螺旋形成趋势。降低AQY和丙氨酸共聚物相对于3 K（I）的计算螺旋含量的主要成分是水合作用。
Conformational energy calculations have been carried out for three hexadecapeptides in water--namely, a copolymer with the sequence acetyl-AAAAKAAAA-KAAAAKA-amide, 3K(I), in both the charged and neutral forms; a neutral peptide with the sequence acetyl-AAQAAAAQAAAAQAAY-amide, AQY; and a 16-residue L-alanine homopolymer with acetyl and amide terminal groups. The conformational energy was a sum of the empirical conformational energy program for peptides (ECEPP/2) potential energy plus continuum hydration free energy. An empirical (JRF) parameter set was used for the hydration free energy, together with an electrostatic contribution to the solvent effect from charged lysines. The computed relatively high helix content of the most probable conformation of charged 3K(I) and the intermediate helix content of AQY agree reasonably well with experimental values. The computed very low helix content of the alanine homopolymer agrees with experiments on block copolymers and on host-guest random copolymers. The calculations suggest that the high helix content computed for 3K(I) is due to the sum of internal and hydration free energies of the lysine residues rather than to a high intrinsic helix-forming tendency of alanine. The principal component lowering the computed helix contents of AQY and the alanine copolymer relative to 3K(I) is hydration.