Tyr61的芳香族侧链对稳定瘦素的结构至关重要

为了研究第61位Tyr（Tyr61）在瘦素（leptin）结构与功能中的作用，构建了2个瘦素突变体Y61F与Y61Q并对其进行了功能分析．Y61F突变体瘦素显示出与野生型瘦素相同的天然凝胶电泳迁移率及相似的折叠效率，而Y61Q突变体瘦素则显示出明显慢的电泳迁移率且较野生型瘦素更难于折叠．受体结合及免疫活性测定显示, Y61F突变体保留了野生型瘦素的大部分生物学活性，而Y61Q突变体仅保留了野生型瘦素16％的受体结合活性及30％的免疫活性．圆二色性分析及二级结构估算表明，Y61F突变体具有与野生型瘦素几乎一样的二级结构组成，而Y61Q突变体的结构则较野生型瘦素更为松散.本研究表明，Tyr61的芳香族侧链被包埋于分子内部的疏水区域中对稳定瘦素结构及其发挥生理功能至关重要，而Tyr61上的羟基在这一过程中并不起重要作用．

Tyr61 Aromatic Side Chain is Critical for Spatial Structure Formation of Leptin

Leptin mutants Y61F and Y61Q were constructed to study the role of the hydroxyl group on the aromatic ring at the center of leptin. Y61F leptin exhibited a nearly identical mobility in native PAGE assay and gave a similar folding yield in in vitro refolding analysis when compared with wild type leptin. Whereas, Y61Q leptin showed a retarded mobility and crippled folding ability. Receptor binding and immune activity assays demonstrated that Y61F leptin maintained most of biological activity of wild type leptin, while Y61Q leptin only retained about 16% of receptor binding activity and 30% of immune activity of wild type leptin. Circular dichroism (CD) analysis indicated that Y61F leptin shared a similar secondary structure profile with wild type leptin, while the structure of Y61Q leptin appeared to be much looser. These results indicate that the buried aromatic side chain of Tyr61 is more critically involved in the folding and activity of leptin beyond the hydroxyl group.