Cold-adaptation and structural prediction of carboxypeptidase from Euphausia superb

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 K_cat/K_m 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.