Improvement of thermostability of cold-active serine alkaline protease from the psychrotrophic bacterium Shewanella sp. strain Ac10 by rational mutagenesis

A serine alkaline protease (SapSh) from a psychrophilic bacterium Shewanella sp. strain Ac10 is a cold-active subtilase with low thermostability [Appl. Environ. Microbiol. 65 (1999) 611–617]. By means of homology modeling with other subtilase structures, we have constructed a mutant SapSh containing an extra salt bridge on its surface that exhibits higher thermostability and even higher Vmax/Km, app value than those of the wild-type SapSh.