|Family type peptidase||C31.001 - porcine reproductive and respiratory syndrome arterivirus-type cysteine peptidase alpha (lactate-dehydrogenase-elevating virus), MEROPS Accession MER0002117 (peptidase unit: 1-155)|
|Content of family||Peptidase family C31 contains polyprotein processing endopeptidases from viruses.|
Identifier created: Perspect.Drug Discov.Des. 6:1-11 (1996)|
Peptidase family C31 contains the papain-like cysteine peptidase alpha (PCP-alpha) of arteriviruses. Arteriviruses are enveloped, positive-strand RNA viruses that contain polycistronic genomes. Their proteins are expressed from the open reading frames (ORF"s) 1a and 1b, that encode two large precursor proteins: the ORF1a protein, and, as a result of ribosomal frame-shifting, the ORF1ab protein. Both precursors are processed by three or four ORF1a-encoded peptidases. The papain-like cysteine peptidase alpha is the most N-terminally-located of an array of three cysteine peptidase domains that have been identified in the N-terminal 500 residues of the arterivirus ORF1a protein (Gorbalenya et al., 2004).
|Active site residues||C76 H147 |
|Active site||The active site residues of family C31 are Cys and His, which form a catalytic dyad. There is a conserved Trp immediately C-terminal to the catalytic Cys (see the Alignment).|
|Activities and specificities||PCP alpha cleaves the polyprotein C-terminal to the catalytic His, producing a 20- to 22-kDa product, non-structural protein 1 (Nsp1alpha). There is a requirement for a substantial portion of the polyprotein to be present C-terminal to the cleavage site in order for cleavage to take place (Gorbalenya et al., 2004). In the equine arteritis virus the would-be catalytic Cys residue is replaced by Leu and the protein is therefore not an active peptidase.|
|Basis of clan assignment||Active site residues for members of this family and family C1 occur in the same order in the sequence: C, H.|