Secretion and autoproteolytic maturation of subtilisin.

The sequence of the cloned Bacillus amyloliquefaciens subtilisin gene suggested that this secreted serine protease is produced as a larger precursor, designated preprosubtilisin [Wells, J. A., Ferrari, E., Henner, D. J., Estell, D. A. & Chen, E. Y. (1983) Nucleic Acids Res. 11, 7911-7925]. Biochemical evidence presented here shows that a subtilisin precursor is produced in Bacillus subtilis hosts. The precursor is first localized in the cell membrane, reaching a steady-state level of approximately equal to 1000 sites per cell. Mutations in the subtilisin gene that alter a catalytically critical residue (i.e., aspartate +32----asparagine), or delete the carboxyl-terminal portion of the enzyme that contains catalytically critical residues, block the maturation of this precursor. This block occurs when these mutant genes are expressed in B. subtilis hosts where the chromosomal subtilisin gene has been deleted. When the mutant B. amyloliquefaciens subtilisins are expressed in B. subtilis hosts that contain an intact chromosomal subtilisin gene, the mutant precursors are processed to a mature form and released to the medium. Such processing, in trans, of the precursor is also demonstrated in vitro by addition of active subtilisin. Thus, the release of subtilisin from the cell membrane is dependent on an autoproteolytic process that appears to be novel among secreted proteins.