ECEPE proteins: a novel family of eukaryotic cysteine proteinases.

Using a variety of fold-recognition methods, a novel eukaryotic cysteine proteinase (ECEPE) family has been identified. This family encompasses sequences from an uncharacterized KOG4621, including the Arabidopsis thaliana guanylyl cyclase-related protein AtGC1. ECEPE proteins are predicted to possess the papain-like cysteine proteinase fold and are evolutionarily linked to C39 peptidases. The presence of the invariant Cys-His-Asp/Asn catalytic triad and the oxyanion-hole glutamine residue characteristic of papain-like cysteine proteases indicate that ECEPE proteins might function as proteases.