AAT

Peptidases are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry. Families are grouped by their catalytic type, the first character representing the catalytic type: A, aspartic; C, cysteine; G, glutamic acid; M, metallo; S, serine; T, threonine; and U, unknown. A clan that contains families of more than one type is described as being of type P. The serine, threonine and cysteine peptidases utilise the catalytic part of an amino acid as a nucleophile and form an acyl intermediate - these peptidases can also readily act as transferases. In the case of aspartic, glutamic and metallopeptidases, the nucleophile is an activated water molecule.

Cysteine peptidases have characteristic molecular topologies, which can be seen not only in their three-dimensional structures, but commonly also in the two-dimensional structures. The peptidase domain is responsible for peptide bond hydrolysis; in Merops this is termed the peptidase unit. These are peptidases in which the nucleophile is the sulphydryl group of a cysteine residue.

Cysteine proteases are divided into clans (proteins which are evolutionary related), and further sub-divided into families, on the basis of the architecture of their catalytic dyad or triad PUBMED:11517925:

• Clan CA contains the families of papain (C1), calpain (C2), streptopain (C10) and the ubiquitin-specific peptidases (C12, C19), as well as many families of viral cysteine endopeptidases.
• Clan CD contains the families of clostripain (C11), gingipain R (C25), legumain (C13), caspase-1 (C14) and separin (C50). These enzymes have specificities dominated by the interactions of the S1 subsite.
• Clan CE contains the families of adenain (C5) from adenoviruses, the eukaryotic Ulp1 protease (C48) and the bacterial YopJ proteases (C55).
• Clan CF contains only pyroglutamyl peptidase I (C15).
• Clan PA contains the picornains (C3), which have probably evolved from serine peptidases and which form the majority of enzymes in this clan.
• Clans PB and CH contain the autolytic cysteine peptidases.

This group of cysteine peptidases belong to MEROPS peptidase family C45 (clan PB(C)). The active site residue for members of this family and family T1 is C-terminal to the autolytic cleavage site. They represent a family of enzymes which catalyse the final step in penicillin biosynthesis PUBMED:2120195.

Alignment

Visualize domain structures

Species distribution