The magnitude of the backbone conformational entropy change in protein folding
The magnitude of the backbone conformational entropy change in protein folding
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DOI：
10.1002/prot.1
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发表时间：
1996-06-01
期刊：
影响因子：
--
通讯作者：
Freire, E
中科院分区：
文献类型：
--
作者：
DAquino, JA;Gomez, J;Freire, E
通过实验和计算分析研究了蛋白质折叠中肽骨架所经历的构象熵变化的大小。实验上，GCN4亮氨酸拉链区域对应的33个氨基酸多肽的两对不同的突变体被用于高灵敏度的微量热分析。每对突变体的不同之处只是在特定的溶剂暴露位置上有丙氨酸或甘氨酸，在这种条件下，稳定性的差异可以归因于未折叠状态的构象熵的差异。所研究的突变体具有不同的稳定性，但在相同的温度下具有相同的去折叠热容变化(Delta C-p)、相同的溶剂相关的去折叠熵(Delta S-solv)和相同的去折叠热(Delta H)。因此，不同突变体之间的稳定性差异可以归因于构象熵的差异。计算研究的目的是生成作为主链二面角Phi和Phi的函数的主链构象的能量分布，该能量分布允许直接计算不同构象的概率分布，从而计算主链的构象熵。实验结果表明，丙氨酸中甲基的存在使肽骨架的构象熵降低了2.46+/-0.2卡/K。相对于甘氨酸的摩尔，与含丙氨酸的多肽中允许的构象数量减少3.4倍一致。从能量分布也得到了类似的结果。计算分析还表明，只要侧链在Beta位没有支化，向侧链添加更多的碳原子只会产生很小的影响。ALA仅进一步降低0.61和0.81卡/K。分别计算了亮氨酸和赖氨酸的主链摩尔。β-分支(Val)的构象熵降幅最大(1.92cal/K)。摩尔小于丙氨酸)。最后，与α-螺旋的展开相关的主干熵变为6.51cal/K。摩尔代表甘氨酸。这些和以前的结果已经允许对与蛋白质折叠相关的构象熵变化进行完整的估计。(C)1996年Wiley-Liss，Inc.
The magnitude of the conformational entropy change experienced by the peptide backbone upon protein folding was investigated experimentally and by computational analysis. Experimentally, two different pairs of mutants of a 33 amino acid peptide corresponding to the leucine zipper region of GCN4 were used for high-sensitivity microcalorimetric analysis. Each pair of mutants differed only by having alanine or glycine at a specific solvent-exposed position under conditions in which the differences in stability could be attributed to differences in the conformational entropy of the unfolded state. The mutants studied were characterized by different stabilities but had identical heat capacity changes of unfolding (Delta C-p), identical solvent-related entropies of unfolding (Delta S-solv), and identical enthalpies of unfolding (Delta H) at equivalent temperatures. Accordingly, the differences in stability between the different mutants could be attributed to differences in conformational entropy. The computational studies were aimed at generating the energy profile of backbone conformations as a function of the main chain dihedral angles phi and phi, The energy profiles permit a direct calculation of the probability distribution of different conformers and therefore of the conformational entropy of the backbone. The experimental results presented in this paper indicate that the presence of the methyl group in alanine reduces the conformational entropy of the peptide backbone by 2.46 +/- 0.2 cal/K . mol with respect to that of glycine, consistent with a 3.4-fold reduction in the number of allowed conformations in the alanine-containing peptides. Similar results were obtained from the energy profiles. The computational analysis also indicates that the addition of further carbon atoms to the side chain had only a small effect as long as the side chains were unbranched at position beta. A further reduction with respect to Ala of only 0.61 and 0.81 cal/K . mol in the backbone entropy was obtained for leucine and lysine, respectively. beta-branching (Val) produces the largest decrease in conformational entropy (1.92 cal/K . mol less than Ala). Finally, the backbone entropy change associated with the unfolding of an alpha-helix is 6.51 cal/K . mol for glycine. These and previous results have allowed a complete estimation of the conformational entropy changes associated with protein folding. (C) 1996 Wiley-Liss, Inc.