PA clan

The PA clan (Proteases of mixed nucleophile, superfamily A) is the largest group of proteases with common ancestry as identified by structural homology. Members have a chymotrypsin-like fold and similar proteolysis mechanisms but sequence identity of <10%. The clan contains both cysteine and serine proteases (different nucleophiles). PA clan proteases can be found in plants, animals, fungi, eubacteria, archaea and viruses.