Osmolyte-driven contraction of a random coil protein
Osmolyte-driven contraction of a random coil protein
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DOI：
10.1073/pnas.95.16.9268
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发表时间：
1998-08-04
影响因子：
11.1
通讯作者：
Bolen, DW
中科院分区：
文献类型：
--
作者：
Qu, YX;Bolen, CL;Bolen, DW
还原和羧酰胺化的核糖核酸酶A（RCAM RNase）的斯托克斯半径特性，确定了这种“无规卷曲”蛋白从水转移到1 M浓度的天然存在的保护渗透剂三甲胺N-氧化物，肌氨酸，蔗糖，脯氨酸和nonprotecting渗透剂尿素。RCAM RNA酶的变性系综在尿素中膨胀，在保护渗透剂中收缩，其程度与蛋白质从水到渗透剂的转移吉布斯能成比例。这种比例表明，蛋白质各个部分的转移吉布斯能之和是变性系综中尺寸变化的原因。RCAM RNA酶从水到保护性渗透剂的转移吉布斯能中的主导项是渗透剂与肽骨架的不利相互作用，而尿素与骨架的有利相互作用在RCAM RNA酶转移到尿素中占主导地位。侧链共同有利于转移到渗透剂，一些保护渗透剂溶解疏水侧链以及尿素，结果表明尿素溶解疏水基团的能力没有什么特别之处。保护渗透剂通过提高变性系综的化学势来稳定蛋白质，并且作用于肽主链的均匀热力学力引起收缩变性系综的附带效应。收缩降低变性状态的构象熵，同时增加疏水基团的密度，这两种效应也有助于保护渗透剂迫使蛋白质折叠的能力。
The Stokes radius characteristics of reduced and carboxamidated ribonuclease A (RCAM RNase) were determined for transfer of this "random coil" protein from water to 1 M concentrations of the naturally occurring protecting osmolytes trimethylamine N-oxide, sarcosine, sucrose, and proline and the nonprotecting osmolyte urea. The denatured ensemble of RCAM RNase expands in urea and contracts in protecting osmolytes to extents proportional to the transfer Gibbs energy of the protein from water to osmolyte, This proportionality suggests that the sum of the transfer Gibbs energies of individual parts of the protein is responsible for the dimensional changes in the denatured ensemble. The dominant term in the transfer Gibbs energy of RCAM RNase from water to protecting osmolytes is the unfavorable interaction of the osmolyte with the peptide backbone, whereas the favorable interaction of urea with the backbone dominates in RCAM RNase transfer to urea. The side chains collectively favor transfer to the osmolytes, with some protecting osmolytes solubilizing hydrophobic side chains as well as urea does, a result suggesting there is nothing special about the ability of urea to solubilize hydrophobic groups. Protecting osmolytes stabilize proteins by raising the chemical potential of the denatured ensemble, and the uniform thermodynamic force acting on the peptide backbone causes the collateral effect of contracting the denatured ensemble, The contraction decreases the conformational entropy of the denatured state while increasing the density of hydrophobic groups, two effects that also contribute to the ability of protecting osmolytes to force proteins to Fold.