人肝再生增强因子CXXC活性结构域的研究

人肝再生增强因子(human augmenter of liver regeneration, hALR)蛋白序列中有一段保守的Cys-Xaa-Xaa-Cys (CXXC)氨基酸序列，针对hALRp的CXXC结构，对hALR分别进行C65A和Q88C突变，表达、纯化突变体蛋白。体外检测hALRp和突变体的黄素腺嘌呤二核苷酸(flavin adenine dinucleotide, FAD)辅助的巯基氧化酶活性，hALR-FAD和hALRQ88C-FAD组与对照组比较有显著差异(P<0.05)，hALR-FAD和hALRQ88C-FAD组之间无差异；hALRC65A-FAD组与对照组比较无差异。结果显示，通过C65A突变将CXXC结构破坏后，该突变体的巯基氧化酶活性完全丧失；通过Q88C突变增加一个CXXC序列后，该突变体的巯基氧化酶活性较hALR-FAD未见明显增加；同时，FAD不仅是hALRp发挥巯基氧化酶活性必须的辅助因子，而且有助于hALRp突变体蛋白的复性。

Study on the CXXC Activity Motif of Human Augmenter of Liver Regeneration

Human augmenter of liver regeneration protein (hALRp) had a fragment of Cys-Xaa-Xaa-Cys(CXXC) amino acid sequence. In order to study the CXXC activity motif ALRp, the amino acid at the position of 65 and 88 in hALRp was exchanged against alanine and cysteine respectively, and then expressed and purified mutagenesis protein. The sulfhydryl oxidase activity of ALRp and its mutagenesis in vitro were detected. The concentration of thiol groups in ALR-FAD and ALRQ88C-FAD group were decreased, and they had significant difference when contrasted to control (P<0.05), but ALRC65A FAD group had no significant difference when contrasted to control. The mutation of C65A that changed the CXXC motif of hALRp deprived all of its activity of sulfhydryl oxidase. The mutation of Q88C that added another CXXC motif in hALR couldn’t improve its activity of sulfhydryl oxidase. At the same time, FAD was a cofactor that was indispensable to the activity of sulfhydryl oxidase of ALR, and it maybe helps the mutation protein at the time of renaturation.