nsp3dPLP2

SARS nsp3 has a domain embedded in between the ADRP and SUD domains that houses the "only" papain-like protease function. Several coronaviruses have two such proteases. The structure reveals a classical cysteine like protease fold that explains the structural basis of cleavage of the polyprotein at the first three sites between nsp1/2, 2/3 and 3/4. In addition, the N proximal portion of the polypeptide adopts a unique ubiquitin-like structure. The function of this domain remains unknown. Several groups have experimentally demonstrated that this region of SARS-nsp3 also exhibits potent de-ubiquitinase activity using model ubiquitin substrates.