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Abstract

Kumamolysin is a thermostable endopeptidase from Bacillus novosp. MN-32, exhibiting maximal proteolytic activity around pH 3. It belongs to the newly identified family of serine- carboxyl proteinases, which also includes CLN2, a human lysosomal homolog recently implicated in a fatal neurodegenerative disease. Kumamolysin and its complexes with two aldehyde inhibitors were crystallized, and their three- dimensional structures were solved and refined with X-ray data to 1.4 Angstrom resolution. As its Pseudomonas homolog, kumamolysin exhibits a Ser/Glu/Asp catalytic triad with particularly short interconnecting hydrogen bonds and an oxyanion hole enabling the reactive serine to attack substrate peptide bonds at quite acidic pH. An additional Glu/Trp pair, unique to kumamolysin, might further facilitate proton delocalization during nucleophilic attack, in particular at high temperature.