engleski

Characterization of the first prokaryotic M49 metallopeptidase reveals a regulatory cysteine residue in the active-site motif

Dipeptidyl peptidase III (DPP III), a member of the metallopeptidase family M49, was considered as an exclusively eukaryotic enzyme involved in intracellular peptide catabolism and pain modulation. New data on genome sequences revealed only in 2003 the first prokaryotic orthologs, which showed low sequence similarity to eukaryotic ones and a cysteine residue in the zinc-binding motif HEXXGH. We cloned and overexpressed the gene encoding putative DPP III from human gut symbiont Bacteroides thetaiotaomicron and biochemically characterized the isolated protein. Substrate specificity and catalytic efficiency of bacterial DPP III for the hydrolysis of preferred synthetic substrate was very similar to that of the human host enzyme. Substitution of Cys450 from the active-site motif H448ECLGH453 by serine did not substantially change the enzymatic activity. However, this residue was wholly responsible for the inactivation effect of sulfhydryl reagents. Molecular modeling of bacterial DPP III indicated seven basic amino acid residues in the local environment of Cys450 as possible cause for its high reactivity. Sequence analysis of 81 bacterial M49 peptidases revealed the conservation of HECLGH motif in 73 primary structures. Majority of proteins lacking an Cys in the active-site motif originated from aerobic bacteria, and by phylogenetic analysis were found to form separate cluster.

anaerobe bacteria ; dipeptidyl peptidase III ; metallopeptidase

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