Family M6


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family M6

NamePeptidase family M6 (immune inhibitor A family)
Family type peptidaseM06.001 - immune inhibitor A peptidase (Bacillus sp.) (Bacillus thuringiensis), MEROPS Accession MER0001164 (peptidase unit: 41-687)
Content of familyPeptidase family M6 contains metalloendopeptidases.
History Identifier created: Biochem.J. 290:205-218 (1993)
Catalytic typeMetallo
Active site residuesH266 E267 H270 D276 
Active siteFamily M6 displays the same HEXXHXXGXXD motif found in family M7. The two histidines and the aspartate are zinc ligands and the glutamate is the is the catalytic residue.
Activities and specificitiesImmune inhibitor A is synthesized as a preproenzyme. The enzyme is capable of digesting two classes of antibacterial humoral factors from insects: cecropins and attacins. Specificity experiments using synthetic cecropin A showed no distinctive cleavage patterns (Dalhammar & Steiner, 1984). A similar enzyme has been found as a major component of the exosporium of the spores of Bacillus cereus (Charlton et al., 1999).
InhibitorsTypically of metallopeptidases immune inhibitor A is inhibited by 1,10-phenanthroline and EDTA, but unusually for a member of subclan MA(M) it is not inhibited by phosphoramidon (Lovgren et al., 1990).
Molecular structureAs with other members of subclan MA(M) there is a conserved methionine and tyrosine C-terminal to the active site motif, forming what is known as a "Met-turn".
Basis of clan assignmentPredicted active site residues for members of this family and thermolysin, the type example for clan MA, occur in the motif HEXXH
Distribution of family Bacteria details  
Archaea details  
Protozoa -  
Fungi details  
Plants details  
Animals details  
Viruses -  
Biological functionsFamily M6 contains a metalloendopeptidase from Bacillus thuringiensis known as immune inhibitor A. This contributes to the virulence of the bacterium, degrading the defensive cecropins and attacin of the immune system of the lepidopteran insects it infects.
Pharmaceutical and biotech relevanceBacillus thuringiensis is widely used in agriculture for the control of insect pests.
Statistics for family M6Sequences:1148
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
immune inhibitor A peptidase (Bacillus sp.)M06.001-
PrtV peptidaseM06.002-
immune inhibitor A2 peptidase (Bacillus sp.)M06.004Yes
family M6 non-peptidase homologuesnon-peptidase homologue-
family M6 unassigned peptidasesunassigned-