Family A9


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family A9

NamePeptidase family A9 (spumapepsin family)
Family type peptidaseA09.001 - spumapepsin (human spumaretrovirus), MEROPS Accession MER0001439 (peptidase unit: 14-180)
Content of familyPeptidase family A9 contains an endopeptidase, spumapepsin.
History Identifier created: Proteolysis in Cell Function, pp13-21, IOS Press, Amsterdam (1997)
Catalytic typeAspartic
Active site residuesD24 
Active siteThe active site Asp of spumapepsin has been identified by site-directed mutagenesis (Konvalinka et al., 1995), and like other viral endopeptidases in clan AA, spumapepsin is assumed to be active only as a dimer with one Asp from each monomer forming the active site dyad. The active site Asp occurs in a Asp-Xaa-Gly motif where Xaa is Ser or Thr. No sequence equivalent to the pepsin (A01.001) 'flap' has been identified.
Activities and specificitiesSpumapepsin processes both the Gag and Pol viral polyproteins. Four cleavages are made, all except one being at asparaginyl bonds. Spumapepsin has also been shown to cleave Pol polyproteins of the yeast Ty1 and Ty3 retrotransposons (Fenyofalvi et al., 1999). Cleavage occurs at neutral pH.
InhibitorsNo inhibitors have been reported.
Molecular structureThe structure of spumapepsin from simian foamy virus has been determined by NMR spectroscopy and shows a retropepsin-like fold (Hartl et al., 2008). Because of this structural similarity, family A9 is included in clan AA. In human foamy virus, spumapepsin is part of the Gag polyprotein, but in simian foamy virus it is part of the Pol polyprotein (Renne et al., 1992). In simian foamy virus, the peptidase domain remains attached to the reverse transcriptase (Hartl et al., 2008).
Basis of clan assignmentActive site residues for members of this family and family A1 occur in the motif D-T/S-G.
Distribution of family Bacteria -  
Archaea -  
Protozoa -  
Fungi -  
Plants details  
Animals details  
Viruses details  
Biological functionsProcessing of the Gag polyprotein by spumapepsin is essential for viral infectivity: without it viral cDNA is not synthesized (Enssle et al., 1997). The Pol polyprotein is processed to release the reverse transcriptase and the integrase.
Statistics for family A9Sequences:18
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
family A9 unassigned peptidasesunassigned-