CONTRIBUTION OF THE SURFACE FREE-ENERGY PERTURBATION TO PROTEIN SOLVENT INTERACTIONS
CONTRIBUTION OF THE SURFACE FREE-ENERGY PERTURBATION TO PROTEIN SOLVENT INTERACTIONS
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DOI：
10.1021/bi00254a029
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发表时间：
1994-12-20
期刊：
影响因子：
2.9
通讯作者：
TIMASHEFF, SN
中科院分区：
文献类型：
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作者：
KITA, Y;ARAKAWA, T;TIMASHEFF, SN
表面张力在20℃下通过毛细管落重法对谷氨酸钠(NaGlu)、盐酸赖氨酸(LysHCl)、天冬氨酸钾(KAsp)、盐酸精氨酸(ArgHCl)、赖氨酰谷氨酸(LysGlu)、精氨酰谷氨酸的水溶液进行测量 (ArgGlu)、硫酸胍、海藻糖、三甲胺 N-氧化物 (TMAO)、二甲基亚砜、2-甲基-2,4-戊二醇（己二醇）和分子量为 200、400、600 和 1000 的聚乙二醇。所有盐和糖都会增加水的表面张力，而最后的盐和糖会增加水的表面张力。 四种化合物可以降低它，其中 2-甲基-2,4-戊二醇降低它的效果最有效，TMAO 效果最差。在 KAsp、ArgHCl、LysGlu 和 ArgGlu 中测量牛血清白蛋白 (BSA) 和溶菌酶的优先水合。除 ArgHCl 中的 BSA 外，在所有情况下都发现优先水合的高值，这表明它们应该稳定蛋白质结构，正如在赖氨酸盐酸盐和谷氨酸钠中发现的那样 [Arakawa, T., and Timasheff, S. N. (1984) J. Biol.化学。 259、4979-4986]。发现 KAsp、NaGlu、LysHCl、ArgGlu 和 LysGlu 中的 BSA 和溶菌酶的表面张力效应与观察到的优先相互作用之间存在相关性，表明由于这些氨基酸盐增加水的表面张力而导致的含蛋白质空腔表面自由能的变化主要有助于观察到的蛋白质化学势的增加。然而，在低浓度的 ArgHCl 中观察到 BSA（而不是溶菌酶）缺乏相关性，其中优先结合接近于零，这表明表面张力效应并不是这些氨基酸盐中蛋白质-溶剂相互作用所涉及的唯一因素。 ArgHCl 与 BSA 的结合可能是通过 Arg 胍基团和肽键之间的氢键发生的，当蛋白质携带净正电荷时（例如溶菌酶的情况），Arg(+) 的亲和力会因静电排斥而降低。由于四种有机溶剂添加剂也会导致蛋白质优先水合，因此它们的优先相互作用与表面自由能扰动之间不存在相关性。因此，在他们的情况下，优先水合必须归因于克服吉布斯吸附等温线预期的优先结合的其他因素。然而，表面张力结果与有机溶剂通过疏水相互作用与蛋白质的结合一致，这至少部分解释了观察到的相互作用的浓度依赖性。
Surface tension measurements were carried out at 20 degrees C by a capillary drop-weight method on aqueous solutions of sodium glutamate (NaGlu), lysine hydrochloride (LysHCl), potassium aspartate (KAsp), arginine hydrochloride (ArgHCl), lysylglutamate (LysGlu), argininylglutamate (ArgGlu), guanidinium sulfate, trehalose, trimethylamine N-oxide (TMAO), dimethyl sulfoxide, 2-methyl-2,4-pentanediol (hexylene glycol), and poly(ethylene glycol)s of molecular weights 200, 400, 600, and 1000. All of the salts and the sugar increased the surface tension of water, while the last four compounds decreased it, with 2-methyl-2,4-pentanediol lowering it most effectively and TMAO being the least effective. The preferential hydration of bovine serum albumin (BSA) and lysozyme was measured in KAsp, ArgHCl, LysGlu, and ArgGlu. The high values of preferential hydration found in all cases, except for BSA in ArgHCl, suggest that they should stabilize protein structure, as had been found for lysine hydrochloride and monosodium glutamate [Arakawa, T., and Timasheff, S. N. (1984) J. Biol. Chem. 259, 4979-4986]. A correlation was found for both BSA and lysozyme in KAsp, NaGlu, LysHCl, ArgGlu, and LysGlu between the surface tension effect and the observed preferential interactions, indicating that the change in the surface free energy of the protein-containing cavity due to the surface tension increase for water by these amino acid salts contributes dominantly to the observed increase in the chemical potential of the protein by their addition. The lack of a correlation observed for BSA, but not lysozyme, in ArgHCl at low concentrations where preferential binding is close to zero suggests, however, that the surface tension effect is not the sole factor involved in the protein-solvent interactions in these amino acid salts. Binding of ArgHCl to BSA, probably through hydrogen bonds between the Arg guanidinium group and peptide bonds, was proposed to occur, the affinity of Arg(+) being reduced by electrostatic repulsion when proteins carry a net positive charge, such as is the case with lysozyme. Since the four organic solvent additives also lead to protein preferential hydration, no correlation exists between their preferential interactions and the surface free energy perturbation. Therefore, in their case, the preferential hydration must be ascribed to other factors that overcome the preferential binding expected from the Gibbs adsorption isotherm. The surface tension results, however, are consistent with the binding of the organic solvents to proteins through hydrophobic interactions, explaining, at least in part, the observed concentration dependence of the interactions.