Family A26


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family A26

NamePeptidase family A26 (omptin family)
Family type peptidaseA26.001 - omptin (Escherichia coli), MEROPS Accession MER0000606 (peptidase unit: 21-317)
Content of familyPeptidase family A26 contains membrane-inserted endopeptidases.
History Identifier created: MEROPS 5.7 (17 December 2001)
Catalytic typeAspartic
Active site residuesD103 D105 D230 H232 
Active siteThe active site residues of the peptidases of family A26 are Asp83, Asp85, Asp210 and His212. A catalytic dyad is formed by Asp210 and His212, whilst Asp83 and Asp85 form a salt bridge (Vandeputte-Rutten et al., 2001). All of the catalytic residues are essential for activity (Kramer et al., 2001).
Activities and specificitiesOmptin (A26.001) shows a preference for cleavage between consecutive basic amino acids, but is capable of cleavage when P1" is a non-basic residue (Dekker, 2004).
InhibitorsA substrate-derived peptide Ala-Arg-D-Arg-Ala inhibits omptin (Dekker et al., 2001).
Molecular structureThe omptin (A26.001) molecule has a ten-stranded anti-parallel beta-barrel structure, resembling a vase (Vandeputte-Rutten et al., 2001). The strands are amphipathic, causing the hydrophilic residues to point into the barrel and the hydrophobic residues to be exposed to the outside. The residues of the catalytic dyad are found on opposite sides of the active site groove at the extracellular top.
Basis of clan assignmentType family of clan AF.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses -  
Biological functionsIt has been suggested that omptin (A26.001) may have a role in an adaptive immune response, enabling survival in vivo. Lundrigan & Webb(1992) have suggested that expression of OmpT may be indicative of the pathogenic potential of E. coli strains. Plasminogen activator Pla from Yersinia pestis (A26.003) has similar implications; it can convert plasminogen into active plasmin, which could mediate the breakdown of fibrin barriers Korhonen et al., 2004, and inactive plasmin inhibitor (I04.023; Kukkonen et al., 2001).
ReviewsKorhonen et al., 2004
Statistics for family A26Sequences:143
Identifiers with PDB entries:2
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
OmpP peptidaseA26.002-
plasminogen activator PlaA26.003Yes
protein E (Salmonella sp.)A26.004-
IcsP peptidase (Shigella flexneri)A26.005-
family A26 non-peptidase homologuesnon-peptidase homologue-
family A26 unassigned peptidasesunassigned-