Cloning and heterologous expression of subtilisin SAPN, a serine alkaline protease from Melghiribacillus thermohalophilus Nari2AT in Escherichia coli and Pichia pastoris

Abstract

The sapN gene, encoding the extracellular subtilisin SAPN, a serine alkaline protease from Melghiribacillus thermohalophilus Nari2AT, was isolated, sequenced, and heterologously expressed in Escherichia coli BL21(DE3)pLysS using pUT57 and pTrc99A vectors and in E. coli BL21-AI™ using the Gateway™ pDEST™ 17 vector. Conversely, three cassettes encoding pre-pro-subtilisin (rSAPN/SP-Pro-M), pro-subtilisin (rSAPN/Pro-M), and the mature-subtilisin (rSAPN/M) were hyperexpressed in Pichia pastoris SMD1168 and X33 using the pPICZαC vector. rSAPNs were purified, characterized, and compared to wild-type SAPN. The deduced amino acid sequences exhibited high similarity with subtilisins from Bacillus strains. The highest sequence identity (96 %) was observed with the Bacillus licheniformis MP1 protease, with a 10-residue difference. Compared to SAPN and untagged rSAPNs, (His)6-tagged enzymes showed the highest activity and stability at alkaline pH and high temperature, the highest hydrolysis degree on crab and shrimp by-products, and the best catalytic efficiency. It was found that His6-rSAPN/SP-Pro-Ms expressed in P. pastoris strains was more active than those produced in E. coli. To initiate structure-function relationships, a 3D-model of the Pro-SAPN was built based on the available structures of common subtilisins. These data constitute a pivotal first step toward the creation of new efficient rSAPNs with enhanced catalytic properties and high potential for biotechnological and industrial uses.