THE PEPTIDE BACKBONE PLAYS A DOMINANT ROLE IN PROTEIN STABILIZATION BY NATURALLY-OCCURRING OSMOLYTES
THE PEPTIDE BACKBONE PLAYS A DOMINANT ROLE IN PROTEIN STABILIZATION BY NATURALLY-OCCURRING OSMOLYTES
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DOI：
10.1021/bi00039a051
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发表时间：
1995-10-03
期刊：
影响因子：
2.9
通讯作者：
BOLEN, DW
中科院分区：
文献类型：
--
作者：
LIU, YF;BOLEN, DW
将氨基酸从水到渗透剂、蔗糖和肌氨酸的转移自由能测量作为渗透剂浓度的函数进行测量。从这些数据中，可以获得氨基酸侧链的转移自由能，并且通过二酮哌嗪（DKP）的溶解度测量来确定肽主链的转移自由能。使用核糖核酸酶 A 的天然和未折叠状态的静态可及表面评估，将暴露于溶剂的侧链和肽主链面积乘以它们的转移自由能并求和，以评估蛋白质的天然和未折叠状态从水到渗透剂溶液的转移自由能。结果再现了在渗透剂存在下确定的蛋白质变性自由能曲线的主要特征。与暴露在水中相比，侧链总体上有利于暴露于渗透剂，从这个意义上说，侧链有利于蛋白质解折叠。反对并超越侧链变性偏好并导致在渗透剂中观察到的蛋白质稳定的主要因素是多肽主链在解折叠时非常不利的暴露。除尿素和盐酸胍溶液外，已确定转移自由能测量的所有有机溶剂（例如二恶烷、乙醇、乙二醇）和溶质（渗透剂）均表现出不利的肽主链转移自由能。肽骨架的不利转移自由能的普遍存在，以及肽骨架单元是蛋白质中数量最多的基团这一事实，使其成为影响稳定和不稳定溶剂中存在的蛋白质构象特征的极其重要的因素。
Transfer free energy measurements of amino acids from water to the osmolytes, sucrose and sarcosine, were made as a function of osmolyte concentration. From these data, transfer free energies of the amino acid side chains were obtained, and the transfer free energy of the peptide backbone was determined from solubility measurements of diketopiperazine (DKP). Using static accessible surface evaluations of the native and unfolded states of ribonuclease A, solvent exposed side chain and peptide backbone areas were multiplied by their transfer free energies and summed in order to evaluate the transfer free energy of the native and unfolded states of the protein from water to the osmolyte solutions. The results reproduced the main features of the free energy profile determined for denaturation of proteins in the presence of osmolytes. The side chains were found collectively to favor exposure to the osmolyte in comparison to exposure in water, and in this sense the side chains favor protein unfolding. The major factor which opposes and overrides the side chain preference for denaturation and results in the stabilization of proteins observed in osmolytes is the highly unfavorable exposure of polypeptide backbone on unfolding. Except for urea and guanidine hydrochloride solutions, it is shown that all organic solvents (e.g., dioxane, ethanol, ethylene glycol) and solutes (osmolytes) for which transfer free energy measurements have been determined exhibit unfavorable transfer free energy of the peptide backbone. The prevalence of the unfavorable transfer free energy of the peptide backbone, and the fact that the peptide backbone unit is the most numerous group in a protein, makes it an extremely important factor in influencing the character of protein conformations existing in both stabilizing and destabilizing solvents.