Family C6


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family C6

Family type peptidaseC06.001 - potato virus Y-type helper component peptidase (potato virus Y), MEROPS Accession MER0000815 (peptidase unit: 276-824)
Content of familyPeptidase family C6 contains cysteine endopeptidases of RNA viruses.
History Identifier created: Biochem.J. 290:205-218 (1993)
Catalytic typeCysteine
Active site residuesC626 H699 
Active siteThe catalytic residues Cys649 and His722 were identified by site-directed mutagenesis of the recombinant tobacco etch virus enzyme expressed in vitro (Oh & Carrington, 1989). No equivalent of Gln152 that forms the anion binding site in papain, or third member of a catalytic triad, has been identified.
Activities and specificitiesPeptidases in family C6 are endopeptidases. The only known peptidase activity of the helper component endopeptidase is cleavage at its own C-terminus that releases it from the viral polyprotein. The preferred sequence at the cleavage site is -Tyr-Xaa-GlyGly- (Carrington & Herndon, 1992).
InhibitorsNo inhibitors have been described.
Molecular structureNo tertiary structure is available from the family at the time of writing. Mutational studies show that the helper component endopeptidase is a three-part molecule in which the peptidase unit is at the C-terminus.
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 details  
Viruses details  
Biological functionsHC-Pro has three functional domains, each of which serves a separate function in viral infectivity: the N-terminal third contributes to viral replication and transmission in aphids, the central domain is required for vascular transport of the virus, and the C-terminal third contains the proteolytic domain. There are indications that the p29 and p48 peptidases of the hypovirulence-associated virus of chestnut blight fungus (in families C7 and C8) are particularly closely related to the helper component peptidase (Verchot-Lubicz, 2004).
Statistics for family C6Sequences:216
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
potato virus Y-type helper component peptidaseC06.001Yes
barley yellow mosaic virus-type helper component peptidaseC06.002-
family C6 non-peptidase homologuesnon-peptidase homologue-
family C6 unassigned peptidasesunassigned-