Neutral proteases have broad application as additives in modern laundry detergents and therefore, thermostability is an integral parameter for effective production of protein crystals. To improve thermostability, the contribution of individual residues of Bacillus cereus neutral protease was examined by site-directed mutagenesis. The Lys11Arg and Lys211Arg mutants clearly possessed improved thermostabilities (Tm were 63 and 61 °C respectively) compared to the wild-type (Tm was 60 °C). MD simulations further revealed that the mutants had low RMSD and RMSF values compared to wild-type BCN indicating increased stability of the protein structure. Lys11Arg mutant particularly possessed the lowest RMSD values due to increased residue interactions, which resulted in enhanced thermostability. The mutants also displayed strong stability to most inhibitors, organic solvents and surfactants after incubation for 1 h. This study demonstrated Lys-Arg mutation enhanced thermostability of BCN and thus provides insight for engineering stabilizing mutations with improved thermostability for related proteins.
Keywords: Bacillus cereus; Neutral protease; Site-directed mutation; Thermostability.