Abstract

β-Lactoglobulin (β-LG) is a member of lipocalin superfamily of transporters for small hydrophobic and hydrophilic molecules. We located the binding sites of citric acid and gallic acid on β-lactoglobulin (β-LG) in aqueous solution at physiological conditions, using spectroscopic methods, thermodynamic analysis and molecular modeling. Thermodynamic parameters ΔH⁰ −9.5 to −6.9 (kJ mol⁻¹), ΔS⁰ 23.9 to 13.6 (J mol⁻¹K⁻¹) and ΔG⁰ −14.5 to −13.6 (kJ mol⁻¹) showed that acid binds protein via ionic contacts with gallic acid forming stronger protein conjugates consistent with theoretical modeling. Different amino acids are involved in gallic acid and citric acid complexation. Protein conformation was altered with reduction of β-sheet from 58% (free protein) to 46–43% and a major increase in α-helix from 11% (free protein) to 29–23% and random coil structure in the acid-protein, indicating a partial protein destabilization.

Communicated by Ramaswamy H. Sarma

摘要

β乳球蛋白（β -LG）是脂质运载蛋白超家族的转运为小的疏水和亲水性分子的成员。我们使用光谱方法、热力学分析和分子建模在生理条件下定位了柠檬酸和没食子酸在水溶液中β-乳球蛋白 ( β- LG)上的结合位点。热力学参数Δ H ⁰ -9.5 至-6.9 (kJ mol ^-1 )、Δ S ⁰ 23.9 至13.6 (J mol ^-1 K ^-1 ) 和Δ G ⁰ -14.5 至-13.6 (kJ mol ^{-1 )}) 表明酸通过与没食子酸的离子接触结合蛋白质，形成与理论模型一致的更强的蛋白质缀合物。不同的氨基酸参与没食子酸和柠檬酸的络合。蛋白质构象发生改变，β-折叠从 58%（游离蛋白质）减少到 46-43%，α-螺旋从 11%（游离蛋白质）增加到 29-23%，酸中的无规卷曲结构蛋白质，表明部分蛋白质不稳定。

由 Ramaswamy H. Sarma 交流