alpha-lytic protease (alpha-LP), a bacterial serine protease of the chymotrypsin family, and similar proteins
This family represents the catalytic domain of alpha-lytic protease (alpha-LP) and its closely-related homologs. Alpha-lytic protease (EC 18.104.22.168; also called alpha-lytic endopeptidase), originally isolated from the myxobacterium Lysobacter enzymogenes, belongs to the MEROPS peptidase family S1, subfamily S1E (streptogrisin A subfamily). It is synthesized as a pro-enzyme, thus having two domains; the N-terminal pro-domain acts as a foldase, required transiently for the correct folding of the protease domain, and also acts as a potent inhibitor of the mature enzyme, while the C-terminal domain catalyzes the cleavage of peptide bonds. Members of the alpha-lytic protease subfamily include Nocardiopsis alba protease (NAPase), a secreted chymotrypsin from the alkaliphile Cellulomonas bogoriensis, streptogrisins (SPG-A, SPG-B, SPG-C, and SPG-D), and Thermobifida fusca protease A (TFPA). These serine proteases have characteristic kinetic stability, exhibited by their extremely slow unfolding kinetics. The active site, characteristic of serine proteases, contains the catalytic triad consisting of serine acting as a nucleophile, aspartate as an electrophile, and histidine as a base, all required for activity. This model represents the C-terminal catalytic domain of alpha-lytic proteases.