The carboxy-terminal tail of Aeromonas sobria serine protease is associated with the chaperone

ASP is the only bacterial protease in the kexin group of the subtilisin family. Previous studies have revealed that the ORF2 protein encoded at the 3′ end of the asp operon is required for ASP to change from a nascent form into an active form in the periplasm. However, the mechanism by which ORF2 makes contact and interacts with ASP in the maturation process remains unknown. The present study examined the effect of mutations in the carboxy-terminal region of ASP on the ASP maturation process. Both deletion-mutation and amino acid-substitution studies have demonstrated that the histidine residue at position 595 (His-595), the sixth residue from the carboxyl terminus of ASP, is highly involved in the generation of active ASP molecules. An analysis by pull-down assay revealed that mutation at His-595 reduces the efficacy of nascent ASP to transition into active ASP by reducing the ability of ASP to make contact and interact with ORF2. Thus, it appears likely that nascent ASP in the periplasm interacts with ORF2 via the carboxy-terminal region, and His-595 of ASP appears to be an indispensable residue in this interaction.