Family C4


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family C4

NamePeptidase family C4 (NIa protease family)
Family type peptidaseC04.001 - nuclear-inclusion-a peptidase (plum pox virus) (plum pox virus), MEROPS Accession MER0001785 (peptidase unit: 2049-2293)
Content of familyPeptidase family C4 contains cysteine endopeptidases of viruses.
History Identifier created: Biochem.J. 290:205-218 (1993)
Catalytic typeCysteine
Active site residuesH2096 D2131 C2201 
Active siteThere is a catalytic triad, His/Asp/Cys (Dougherty et al., 1989).
Activities and specificitiesThere is a preference for cleavage of GlnGly bonds in the processing of the viral polyprotein, similar to that in family C3.
InhibitorsNo specific inhibitors of peptidases in this family have been described at the time of writing, but there is inhibition by general thiol-blocking compounds including TLCK and TPCK.
Molecular structureThe structure of the tobacco etch virus enzyme (Phan et al., 2002) shows that the molecules of the peptidases in family C4, like others in clan PA, contain a pair of beta-barrels at right-angles, with the catalytic residues between them.
Basis of clan assignmentActive site residues for members of this family and family S1 occur in the same order in the sequence: H, D, C/S.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses details  
Biological functionsThe type peptidase of family C4 is nuclear-inclusion-a endopeptidase (plum pox virus), also known as the NIa protease.The NIa proteases are required for the processing of the potyviral proproteins.
Pharmaceutical and biotech relevanceBecause of its stringent cleavage specificity, tobacco etch virus NIa protease has proved to be a valuable reagent for cleavage of recombinant fusion proteins at glutaminyl bonds (e.g. Kapust et al., 2002).
Statistics for family C4Sequences:217
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
nuclear-inclusion-a peptidase (plum pox virus)C04.001-
potato virus Y-type NIa peptidaseC04.002-
tobacco vein mottling virus-type NIa peptidaseC04.003-
tobacco etch virus NIa peptidaseC04.004Yes
Ornithogalum mosaic virus NIa peptidaseC04.005-
yam mosaic virus NIa peptidaseC04.006-
shallot potyvirus NIa peptidaseC04.007-
bean yellow mosaic virus-type NIa peptidaseC04.008-
Papaya ringspot virus NIa peptidaseC04.009-
pea seed-borne mosaic virus NIa peptidaseC04.010-
Johnson grass mosaic virus NIa peptidaseC04.011-
rye grass mosaic virus NIa peptidaseC04.012-
sweet potato mild mottle virus NIa peptidaseC04.013-
potato virus A NIa peptidaseC04.014-
family C4 non-peptidase homologuesnon-peptidase homologue-
family C4 unassigned peptidasesunassigned-