Family M27


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family M27

Family type peptidaseM27.001 - tentoxilysin (Clostridium tetani), MEROPS Accession MER0001174 (peptidase unit: 117-457)
Content of familyPeptidase family M27 contains highly selective metalloendopeptidases.
History Identifier created: Methods Enzymol. 248:183-228 (1995)
The bacteria Clostridium tetani and Clostridium botulinum have long been notorious for their ability to produce the diseases tetanus and botulism. Major symptoms of both conditions are forms of paralysis caused by neurotoxins that are the metallopeptidases of family M27. In recent times the value of the C. botulinum neurotoxin bontoxilysin A (M27.002, as Botox) for therapeutic and cosmetic applications has become well recognised (Ting & Freiman, 2004).
Catalytic typeMetallo
Active site residuesH233 E234 H237 E271 R372 Y375 
Active siteThe peptidases of family M27 are amongst the HEXXH" metallopeptidases in clan MA. In these, the two histidines of the HEXXH motif are ligands of a single zinc atom, and the glutamate has a catalytic role. A more C-terminal glutamate acts as the third ligand of the zinc atom. In tentoxilysin, Tyr374 also has a catalytic function, and Arg371 stabilizes the transition state (Hanson & Stevens, 2000).
Activities and specificitiesThe only known protein substrate of tentoxilysin (M27.001) is the 120-residue vesicle-associated membrane protein (VAMP) better termed synaptobrevin. Several forms of synaptobrevin are known. Tentoxilysin cleaves synaptobrevin 2 at the Gln76Phe77 bond whereas bontoxilysin, which is also highly selective, cleaves synaptobrevin at the Gln60Lys61 bond (Montecucco & Rossetto, 2004; Montecucco & Tonello, 2004).
InhibitorsPotent inhibitors of bontoxilysin have been developed for possible therapeutic use (Blommaert et al., 2004).
Molecular structureThe tertiary structure of bontoxilysin shows a seven-stranded beta-sheet and three helices (including two that carry the zinc ligands) that are in topologically equivalent positions to those in thermolysin (Hanson & Stevens, 2000). Structural data are also available for the C-terminal domain that has a ganglioside-binding site, and is responsible for the targeting of the toxin in vivo (Fotinou et al., 2001).
Basis of clan assignmentProtein fold of the peptidase unit for members of this family resembles that of thermolysin, the type example for clan MA.
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses details  
Biological functionsThe clostridial neurotoxins are significant to mankind because of their central role in the diseases tetanus and botulism. Both neurotoxins cause motor paralysis by blocking acetylcholine release at neuromuscular junctions. It is notable that despite their generally similar mechanisms of action, tentoxilysin causes tetanus (muscular rigidity) but bontoxilysin causes flaccid muscle paralysis. Bontoxilysin is synthesized as a 150-kDa precursor that is activated by cleavage to a disulfide-linked heterodimer with an N-terminal light chain (50 kDa) and a C-terminal heavy chain (100 kDa). The heavy chain has a high and specific affinity for membrane constituents of neurons, whereas the light chain contains the endopeptidase active site. The toxin accumulates in the bacterial cell until it lyses, and is then internalized by neuron cells into endosome-like vesicles. The toxin passes to the cytoplasm where the free light chain is able to cleave synaptobrevin, a crucial component of the neuroexocytosis apparatus.
Pharmaceutical and biotech relevanceAs Botox, bontoxilysin A is widely used in medical procedures for local paralysis of sets of muscles.
Statistics for family M27Sequences:44
Identifiers with PDB entries:3
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
VAMP-cleaving peptidase (Weissella oryzae)M27.003-
family M27 non-peptidase homologuesnon-peptidase homologue-
family M27 unassigned peptidasesunassignedYes