南极磷虾羧肽酶的适冷特性及蛋白质结构预测

Cold-adaptation and structural prediction of carboxypeptidase from Euphausia superb

  • 摘要: 研究南极磷虾羧肽酶的适冷特性,探讨其在催化反应过程中应对低温环境的机理,对酶类分子改造等基础学研究及实际生产应用具有一定意义。本研究首先比较了南极磷虾羧肽酶及牛(胰)羧肽酶的动力学,对其适冷性进行了分析,接着采用生物信息学方法,对其理化性质和氨基酸序列进行比对,并进行二级、三级结构预测,对南极磷虾羧肽酶的结构与适冷性关系进行探讨。结果显示,在4和30 °C下,南极磷虾羧肽酶催化效率及对底物的亲和性均高于常温下的牛(胰)羧肽酶,更能适应低温环境。通过结构分析预测,南极磷虾羧肽酶氨基酸序列与河鳌虾等物种同源性较高,活性位点、Zn结合位点等存在保守性;不同的是与其他恒温动物相比南极磷虾羧肽酶含有更高比例的Asp和较低比例的Pro、Arg、Phe,可能致使其蛋白质分子内相互作用减弱,分子柔性增强;二级元件中松散的无规则卷曲占比相对较高,使得南极磷虾羧肽酶三级结构呈现出活性中心更暴露、整体结构更松散的状态。南极磷虾羧肽酶具有一定的适冷性,酶分子各级蛋白结构基于降低分子间作用力、提高分子柔性和减少活性位点空间位阻等,为其应对低温环境并保持较高效的催化能力起到了一定的作用。

     

    Abstract: The study of the cold-adapted characteristics of Euphausia superb carboxypeptidase and its mechanism of responding to low temperature in the catalytic reaction process was of certain significance to the fundamental research of enzymatic molecular transformation and practical production and application. This paper studied the cold-adaptation of carboxypeptidase from E. superb and discussed its cold-adaptation mechanism, in an attempt to provide support for basic research on molecular modification and broaden its commercial application. The cold-adaptation of carboxypeptidase from E. superb was initially examined by comparing its thermodynamic activation parameters with its counterparts from bovine. Then the cold-adaptation mechanism was discussed with the full gene and predicted structure based on bioinformatics. The results showed the catalytic efficiency Kcat/Km and affinity to substrate of E. superb carboxypeptidase were higher than its counterparts of bovine at 4 °C and 30 °C respectively and revealed its cold-adaptation behavior. The amino acid sequence of E. superb carboxypeptidase was highly homologous with many species, such as Astacus astacus, as seen in the result of sequence alignment. The active site and Zn binding site were also proved to have conservativeness. Its cold-adaptation may be attributed to the following attributes. The proportions of certain residues were critical in cold-adaptation behavior, such as a higher proportion of Asp and lower proportions of Pro, Arg and Phe compared with its warm-counterparts. It could probably diminish the number of intra-molecular interaction resulting in improved structural flexibility. Furthermore, higher proportion of loose random coils and reduced steric hindrance might be also the key factors promoting its cold-adaptation. The carboxypeptidase from E. superb was prone to have cold-adaptation behavior. The special molecular cold-adaptation strategies to low temperature were revealed as, but not limited to, different proportions of certain residues, more loose random coils and reduced steric hindrance, all of which promoted the catalytic reaction.

     

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