A CLN2-Related and Thermostable Serine-Carboxyl Proteinase, Kumamolysin: Cloning, Expression, and Identification of Catalytic Serine Residue

The gene encoding kumamolysin, a thermostable pepstatin-insensitive carboxyl proteinase, was cloned and expressed, (i) Kumamolysin was synthesized as a large precursor consisting of two regions: amino-terminal prepro (188 amino acids) and mature proteins (384 amino acids), (ii) The deduced amino acid sequence of the mature region exhibited high similarity to those of such bacterial pepstatin-insensitive enzymes as Pseudomonas carboxyl proteinase (PSCP; EC 3.4.23.37, identity = 37%), Xanthomonas carboxyl proteinase (XCP; EC 3.4.23.33, identity = 36%), and human CLN2 gene product (identity = 36%), which is related to a fatal neurodegenerative disease, (iii) The presumed catalytic triad, Glu78, Asp82, Ser278 [three-dimensional structure of PSCP: Wlodawer, A. et al. (2001) Nature Struct BioL, 8, 442–446], was found to be conserved in the amino acid sequence of kumamolysin. (iv) Kumamolysin was inactivated by such aldehyde-type inhibitors as Ac-Ile-Pro-Phe-CHO (Ki = 0.7 ± 0.14 μM). In PSCP, it has been clarified that these inhibitors form a hemiacetal linkage with the catalytic serine residue and inactivate the enzyme, (v) Mutational analysis of the Ser278 residue revealed that the mutant lost both auto-processing activity and proteolytic activity. These results strongly suggest that kumamolysin has a unique catalytic triad consisting of Glu78, Asp82, and Ser278 residues, as previously observed for PSCP.