Secretory expression and site‐directed mutagenesis studies of the winter flounder skin‐type antifreeze polypeptides

Winter flounder contains both liver‐type, extracellular antifreeze polypeptides (wflAFPs) and less active skin‐type, intracellular antifreeze polypeptides (wfsAFPs). The lower activity of wfsAFPs might be due to their lack of complete ice‐binding motifs ‘‐K–DT‐’. In order to test the functional role of this putative ice‐binding motif, mutations were introduced into the N‐terminal or C‐terminal regions of wfsAFP‐2, which lack any presumptive ice‐binding motifs. The wild‐type and mutant wfsAFP‐2 were secreted in Escherichia coli culture media as mature antifreeze proteins and purified to homogeneity. Surprisingly, the antifreeze activity decreased with the introduction of ice‐binding motifs. However, there was a corresponding decrease in α‐helical content as well as thermal stability and this would suggest a compromise in retaining helical structure with the presence of ice‐binding motifs. These studies have brought new definitions of the roles of ice‐binding motif residues in type I antifreeze proteins.

Secretory expression and site‐directed mutagenesis studies of the winter flounder skin‐type antifreeze polypeptides Journal Articles