Family S50


Summary Holotypes Alignment Tree Genomes Literature Architecture

Summary for family S50

Family type peptidaseS50.001 - infectious pancreatic necrosis birnavirus Vp4 peptidase (infectious pancreatic necrosis virus), MEROPS Accession MER0002124 (peptidase unit: 455-721)
Content of familyFamily S50 contains polyprotein processing endopeptidases from double-stranded RNA viruses.
History Identifier created: MEROPS 5.00 (20 April 2000)
Birnaviruses are double-stranded DNA viruses with two genome segments designated A and B. Segment A includes two overlapping open reading frames, the larger of which encodes a polyprotein. The protein known as VP4 is the polyprotein processing enzyme (#S50.001#).
Catalytic typeSerine
Active site residuesS633 K674 
Active siteThe active site Ser, Lys dyad has been identified by site-directed mutagenesis in VP4 from the infectious pancreatic necrosis virus (Lejal et al., 2000; Petit et al., 2000). Unusually, processing occurred when the active site serine was replaced by cysteine (Birghan et al., 2000); in most peptidases replacing the residue carrying the nucleophile would lead to an inactive protein.
Activities and specificitiesVP4 probably cleaves the polyprotein at two sites. In the Drosophila X virus, one site (Ser500Ala) has been experimentally determined, and the second (Ser723Ala) is speculative (Chung et al., 1996). VP4 also processes pVP2 to VP2 at four AlaAla bonds (Chevalier et al., 2004).
InhibitorsIt has been reported that polyprotein processing in birnaviruses is resistant to inhibitors of all protein classes (cited in Gorbalenya & Mundt, 2004).
Molecular structureThe tertiary structure has been determined for the VP4 protein from infectious pancreatic necrosis virus (Lee et al., 2007) and shows a structure that is distantly related to family S16, which also possesses a Ser-Lys dyad separated by a similar number of residues. This relationship had previously been proposed by Birghan et al., 2000. Consequently the family S50 is included in clan SJ. However, unlike in family S16, there is no requirement for ATP.
Basis of clan assignmentActive site residues for members of this family and family S24 occur in the same order in the sequence: S, K.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses details  
Biological functionsVP4 processes the viral polyprotein and releases itself and the major capsid proteins pVP2 and VP3 (Petit et al., 2000). VP2 is also involved in maturation of the VP2 protein (Chevalier et al., 2004).
Statistics for family S50Sequences:24
Identifiers with PDB entries:2
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Other databases INTERPRO IPR002664
PFAM PF01768
Peptidases and Homologues MEROPS ID Structure
infectious pancreatic necrosis birnavirus Vp4 peptidaseS50.001-
avian infectious bursal disease birnavirus Vp4 peptidaseS50.002-
Drosophila X virus Vp4 peptidaseS50.003-
blotched snakehead birnavirus Vp4 peptidaseS50.004-
Family S50 non-peptidase homologuesnon-peptidase homologue-
Family S50 unassigned peptidasesunassigned-