Crystallin proteins undergo various posttranslational modifications with aging of eye lens. Oxidation of tryptophan (Trp) residues of a major γ-crystallin namely human γD-crystallin (HGD) was found to be inhibited by a naturally occurring flavonoid hesperetin at relatively low concentration mostly due to its antioxidant activity. Further the molecular interactions between HGD and hesperetin were elucidated on the basis of the quenching of Trp fluorescence of the protein by the flavonoid. Ground state complexation between HGD and hesperetin caused static quenching of the Trp fluorescence of HGD. Binding and quenching constants were in the order of (103- 104 M-1). Energy transfer from protein to hesperetin was suggested by FRET calculations. Thermodynamic parameters reveal significant hydrophobic association between the protein and hesperetin. Synchronous fluorescence and CD spectroscopic results had ruled out conformational changes in the protein due to binding of hesperetin. Docking studies suggested the proximity of hesperetin with Trp 42, which largely corroborates our experimental findings.

中文翻译：

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橙皮素对人γD-晶状体蛋白色氨酸残基翻译后氧化的保护作用：分子水平研究。

晶状体蛋白会随着眼球的老化而经历各种翻译后修饰。发现主要的γ-晶状蛋白，即人γD-晶状蛋白（HGD）的色氨酸（Trp）残基被较低浓度的天然黄酮类橙皮素抑制，主要是由于其抗氧化活性。此外，基于黄酮类化合物对蛋白质的Trp荧光的猝灭，阐明了HGD和橙皮素之间的分子相互作用。HGD和橙皮素之间的基态络合导致HGD Trp荧光的静态猝灭。结合常数和猝灭常数为（103-104 M-1）。FRET计算表明从蛋白质到橙皮素的能量转移。热力学参数显示蛋白质和橙皮素之间显着的疏水性缔合。同步荧光和CD光谱分析结果排除了由于橙皮素的结合而引起的蛋白质构象变化。对接研究表明橙皮素与Trp 42接近，这在很大程度上证实了我们的实验结果。