Family S81


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family S81

Family type peptidaseS81.001 - destabilase (Hirudo medicinalis), MEROPS Accession MER0003393 (peptidase unit: 23-133)
Content of familyFamily S81 contains isopeptidases.
History Identifier created: MEROPS 9.8 (17 December 2012)
Family S81 contains the bifunctional enzyme destabilase (S81.001) from the medicinal leech (Hirudo medicinalis) and other invertebrates. The family is also known as 'i-lyz' for 'invertebrate lysozyme'.
Catalytic typeSerine
Active site residuesS49 K58 
Active siteDestabilase has two active sites each with a different catalytic activity, that of a lysozyme and that of an isopeptidase. Mutagenesis studies have shown that the lysozyme activity is dependent upon Glu14 and Asp26, whereas the isopeptidase activity requires a serine/lysine catalytic dyad, namely Ser29 and Lys38 (Zavalova et al., 2012).
Activities and specificitiesAs a lysozyme, destabilase cleaves the beta-(1,4)-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine of the peptidoglycan of bacterial cell walls. The isopeptidase activities include hydrolysing epsilon-(gamma-Glu)-Lys crosslinks between Glu and Lys in a stabilized fibrin (Baskova & Nikonov, 1991) and similar isopeptide bonds found in the cross-linking peptide of peptidoglycan in bacterial cell walls (Joskova et al., 2009).
Molecular structureThe tertiary structure of lysozyme from Tapes japonica has been determined, and shows that the enzyme exists at low salt concentrations as a dimer. At high salt concentrations, monomers form and the chitinase activity increases (Goto et al., 2007).
Distribution of family Bacteria details  
Archaea -  
Protozoa details  
Fungi -  
Plants details  
Animals details  
Viruses details  
Biological functionsBy disrupting the cell wall of a Gram positive bacterium, lysozyme is bactericidal and protects against infection. Destabilase has been shown to prevent coagulation thereby allowing the leech to feed on its host for longer (Baskova et al., 1995 ). Coagulation is prevented not only by breakdown of fibrin crosslinks but also by preventing platelet aggregation (Baskova et al., 2000). Destabilase is synthesized as a precursor with an N-terminal activation peptide (Fradkov et al., 1996) and is secreted by the salivary glands (Baskova et al., 2001).
ReviewsZavalova & Baskova, 2004
Statistics for family S81Sequences:366
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 S81 non-peptidase homologuesnon-peptidase homologue-
family S81 unassigned homologueunassigned-