Family A5


Summary Holotypes Alignment Tree Genomes Literature

Summary for family A5

NamePeptidase family A5 (thermopsin family)
Family type peptidaseA05.001 - thermopsin (Sulfolobus acidocaldarius), MEROPS Accession MER0001319 (peptidase unit: 32-330)
Content of familyPeptidase family A5 contains an endopeptidase.
History Identifier created: Proteolysis in Cell Function, pp13-21, IOS Press, Amsterdam (1997)
Thermopsin (A05.001) was first described by Lin & Tang (1990) and Fusek et al. (1990).
Catalytic typeAspartic
Active siteThe active site residues in thermopsin are unknown. Because of its low pH optimum (pH 2), thermopsin has tentatively been assumed to be an aspartic peptidase. No aspartic residues are completely conserved in the family, but some of the known homologues may not be active peptidases. The residues Asp228, Asp257 and Asp302, are almost completely conserved, and so are candidate active site residues. Acid-acting peptidases are not necessarily aspartic peptidases, as is shown by families G1 and S53, and it may be significant that Gln109, Asn111, Gln128 and Asn148 are completely conserved in the family.
Activities and specificitiesThermopsin has a pH optimum of 2.0 and is mainly active from pH 1-5. It is most active at 80°C, although activity is present from 40 to 100° (Tang & Lin 2004). Sites of cleavage of the oxidized insulin B-chain and hemoglobin suggest a specificity similar to that of pepsin with a preference for hydrophobic residues in P1 and P1".
Molecular structureThe tertiary structure has not been solved for any member of the family.
Basis of clan assignmentProtein fold and active site residues are not known for any members of this family.
Distribution of family Bacteria -  
Archaea details  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses -  
Biological functionsSulfolobus acidocaldarius is a thermophilic archaean isolated from the geyser Old Faithful in the Yellowstone National Park. Thermopsin is probably important for the nutrition of the organism. It is synthesized with an N-terminal propeptide, and the LeuPhe activation cleavage is probably autolytic. The protein is highly glycosylated and is attached to the cell surface by an unknown mechanism (Tang & Lin 2004).
ReviewsTang & Lin (2004)
Statistics for family A5Sequences:102
Identifiers with PDB entries:0
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
family A5 unassigned peptidasesunassigned-