UREA UNFOLDING OF PEPTIDE HELICES AS A MODEL FOR INTERPRETING PROTEIN UNFOLDING
UREA UNFOLDING OF PEPTIDE HELICES AS A MODEL FOR INTERPRETING PROTEIN UNFOLDING
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DOI：
10.1073/pnas.92.1.185
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发表时间：
1995-01-03
影响因子：
11.1
通讯作者：
BALDWIN, RL
中科院分区：
文献类型：
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作者：
SCHOLTZ, JM;BARRICK, D;BALDWIN, RL
为了提供一个模型系统来理解尿素对蛋白质α-螺旋的展开如何促进蛋白质变性，我们测量了一系列具有重复序列Ala-Glu-Ala-Ala-Lys-Ala的螺旋多肽的尿素展开，其链长从14个到50个残基不等。在0℃测定了螺旋-螺旋转变理论的Zimm-Bragg模型(S)的螺旋传播参数与尿素摩尔浓度([尿素])的关系，发现ln S与[尿素]呈线性关系。用尿素与多肽相互作用的结合位模型和溶剂交换模型对结果进行了拟合，这两种热力学模型都能很好地描述数据，但我们不能看出每个模型对数据的拟合能力有什么不同。因此，一个线性关系S=ln S(0)-(m/rt)·[尿素]符合α-螺旋展开的数据，就像其他人发现的蛋白质展开的数据一样。当这里确定的α-螺旋展开的m值乘以部分螺旋蛋白质分子中螺旋残基的数量时，得到的值与观察到的这些蛋白质的m值在2的因子内一致。这一结果表明，尿素和多肽之间的相互作用是尿素对蛋白质变性作用的主要原因，正如一些小分子模型研究所预测的那样。
To provide a model system for understanding how the unfolding of protein alpha-helices by urea contributes to protein denaturation, urea unfolding was measured for a homologous series of helical peptides with the repeating sequence Ala-Glu-Ala-Ala-Lys-Ala and chain lengths varying from 14 to 50 residues. The dependence of the helix propagation parameter of the Zimm-Bragg model for helix-coil transition theory (s) on urea molarity ([urea]) was determined at O degrees C with data for the entire set of peptides, and a linear dependence of ln s on [urea] was found. The results were fitted by the binding-site model and by the solvent-exchange model for the interaction of urea with the peptides, Each of these thermodynamic models is able to describe the data quite well and we are not able to discern any difference between the ability of each model to fit the data. Thus a linear relation, In s = ln s(0) - (m/RT).[urea], fits the data for alpha-helix unfolding, just as others have found for protein unfolding. When the m value determined here for alpha-helix unfolding is multiplied by the number of helical residues in partly helical protein molecules, the resulting values agree within a factor of 2 with observed m values for these proteins. This result indicates that the interaction between urea and peptide groups accounts for a major part of the denaturing action of urea on proteins, as predicted earlier by some model studies with small molecules.