Family C31


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family C31

Family type peptidaseC31.001 - porcine reproductive and respiratory syndrome arterivirus-type cysteine peptidase alpha (lactate-dehydrogenase-elevating virus), MEROPS Accession MER0002117 (peptidase unit: 1-155)
Content of familyPeptidase family C31 contains polyprotein processing endopeptidases from viruses.
History 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).
Catalytic typeCysteine
Active site residuesC76 H147 
Active siteThe 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 specificitiesPCP 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.
Molecular structure
Basis of clan assignmentActive site residues for members of this family and family C1 occur in the same order in the sequence: C, H.
Distribution of family Bacteria -  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses details  
Biological functionsThe Nsp1 alpha peptidase (Nsp1 peptidase in equine arteritis virus), which contains PCP alpha, assists the main Nsp4 serine peptidase (S32.001) in the maturation of the replicase polyprotein (Ziebuhr et al., 2000). It has been suggested that there may be a secondary non-peptidase role associated with the PCP alpha domain, because many residues have been conserved in the equine arteritis virus despite replacement of the catalytic Cys (den Boon etal, 1995).
ReviewsGorbalenya et al. (2004)
Statistics for family C31Sequences:19
Identifiers with PDB entries:1
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
porcine reproductive and respiratory syndrome arterivirus-type cysteine peptidase alphaC31.001-
family C31 non-peptidase homologuesnon-peptidase homologue-
family C31 unassigned peptidasesunassignedYes