Protein engineering of the Bacillus alcalophilus PB92 ATCC 31408 alkaline protease (SBA) was performed
to obtain enzymes with improved cold adaptation. The activity of SBA at low temperature was enhanced
through direct evolution using error-prone polymerase chain reaction. Two mutation sites, Glu110Ala
and Glu134Ala, were obtained in SBA. To identify the mutation of amino acids in E110A/E134A related
to its activity at low temperature, single mutants E110A and E134A were obtained via site-directed
mutagenesis. The kcat/Km values of the mutants E110A, E134A and E110A/E134A at 10 ◦C were 1.5-, 2.2-
and 2.7-fold higher, respectively, than that of the wild-type. Through the three-dimensional structure
analysis, it was indicated that E110A/E134A showed an improved activity at low-temperature condition
as a result of the disrupted hydrogen bond, increased protein hydrophobicity, and decreased calcium
affinity. The findings of this study provides the theoretical basis and background data for improvement
of the cold adaptation in SBA by protein engineering