We carrited out enzymatic and molecular biological investigations on microbial pepstatin-insensitive carboxyl proteinases (PSCP, XSCP, kumamolisin, and J-4) and their mammalian homologue, the CLN2 gene product (CLN2 protein), which is related to the fatal neurodegenerative disease. Compared these results with the data from structural analyses of PSCP and kumamolisin, we clarified their structures and novel catalytic mechanism and discussed on their molecular evolution, too.
SUMMARY IN 2001:
(i) Conserved serine residues
The conserved serine residues among five enzymes (PSCP, XSCP, kumamolisin, J-4, and the CLN2 protein) were elucidated to be involved in the catalytic residues by their site-directed mutagenesis studies.
(ii) Structural analysis of PSCP and its catalytic mechanism
Structural analysis has revealed that a novel type of catalytic triad composed of Ser287, GIu80, and Asp84 residues is involved in its catalytic function. They were confirmed to be the catalytic residues of PSCP by
site-directed mutagenesis and inhibitor studies.
(iii) New inhibitors for kumamolisin and its application
Novel type of inhibitors were designed and synthesized, and they were used for structural analysis of kumamolisin.
SUMMARY IN 2002:
(i) Structural analysis of prepro-PSCP
S287A mutant was expressed as the insoluble prepro-protein, and the refolded enzyme did not show any autocatalytic processing- and proteinase-activity. These results strongly suggested that Ser287 residue was involved in the catalytic residues. Structural analysis of the S287A mutant is now in progress.
(ii) Catalytic residues in kumamolisin
Based on the structure of kumamolisin, Glu32 and Trp129 residues were suggested to be an unique catalytic residues in kumamolisin molecule. The k_<cat>/K_m values of the E32A and W129A mutants were about 6 and 4 % of that of the control, indicating that both residues were involved in the catalytic function.
(iii) Structural analysis of the CLN2 protein
The CLN2 protein was elucidated to have a substrate-binding site consisting of six subsites (S3-S3') by kinetics analysis. Structural analysis of the CLN2 protein expressed in silkworm pupae is now in progress. Less