Family C53


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family C53

Family type peptidaseC53.001 - pestivirus Npro peptidase (classical swine fever virus), MEROPS Accession MER0002219 (peptidase unit: 1-168)
Content of familyFamily C53 contains endopeptidases that process the Pestivirus p20 polyprotein.
History Identifier created: MEROPS 5.3 (4 December 2000)
Pestiviruses are single-stranded RNA viruses in which the genome contains one long open reading frame of about 4000 codons. This encodes the p80 polyprotein which is processed into individual proteins by a combination of virally-encoded and host peptidases. The two virally-encoded peptidases are the NS3 endopeptidase (S31.001), and the NPro protein (C53.001, also known as p20) (Wiskerchen & Collett, 1991).
Catalytic typeCysteine
Active site residuesH49 C69 
Active siteThe active site triad has been identified by site-directed mutagenesis (Rumenapf et al., 1998).
Activities and specificitiesThe NPro endopeptidase has only one known peptidase activity: to release itself from the N-terminus of the p20 polyprotein by an autolytic cleavage of the Cys168Gly bond in cys (Stark et al., 1993).
Molecular structureThe NPro endopeptidase was initially thought to have a papain-like structure with a Cys, His catalytic dyad (Gorbalenya et al., 1991), but the predicted histidine was shown not to be essential for activity and the triad identified is unlike that known for any other cysteine peptidase (Rumenapf et al., 1998).
Basis of clan assignmentActive site residues occur in the order H, C in the sequence which is unlike that in any other family.
Distribution of family Bacteria -  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals details  
Viruses details  
Biological functionsPestiviruses cause diseases in cattle (viral diarrhea), sheep (border disease) and pigs (classical swine fever). Autolytic release of the NPro endopeptidase exposes the viral capsid protein at the N-terminus of the polyprotein which may be an important step for further processing. The released NPro protein has no known function. In a lethal form of bovine viral diarrhea, known as mucosal disease, there is a second copy of the NPro protein next to the NS3 protein, and two cleavages occur (Meyers et al., 1992). The NPro peptidase has been shown to inhibit interferon production by infected cells (La Rocca et al., 2005).
Statistics for family C53Sequences:49
Identifiers with PDB entries:2
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
pestivirus Npro peptidaseC53.001Yes
pestivirus strain D32/00_HoBi Npro peptidaseC53.002Yes
non-peptidase homologue-
family C53 unassigned peptidasesunassigned-