Identification of the active site of legumain links it to caspases, clostripain and gingipains in a new clan of cysteine endopeptidases

We show by site-directed mutagenesis that the catalatic residues of mammali an legumain, a recently discovered lysosomal asparaginycysteine endopeptida se, form a catalytic dyad in the motif His-Gly-spacer-Ala-Cys. We note that the same motif is present in the caspases, aspartate-specific endopeptidas es central to the process of apoptosis in animal cells, and also in the fam ilies of clostripain and gingipain which are arginyl/lysyl endopeptidases o f pathogenic bacteria. We propose that the four families have similar prote in folds, are evolutionarily related in dan CD, and have common characteris tics including substrate specificities dominated by the interactions of the S1 subsite. (C) 1998 Federation of European Biochemical Societies.