Structural Determinants of the Specificity for Synaptic Vesicle-associated Membrane Protein/Synaptobrevin of Tetanus and Botulinum Type B and G Neurotoxins
Journal of Biological Chemistry
Tetanus and botulinum neurotoxins type B and G are zinc-endopeptidases of remarkable specificity. They recognize and cleave a synaptic vesicle-associated membrane protein (VAMP)/synaptobrevin, an essential protein component of the vesicle docking and fusion apparatus. VAMP contains two copies of a nine-residue motif, also present in SNAP-25 (synaptosomal-associated protein of 25 kDa) and syntaxin, the two other substrates of clostridial neurotoxins. This motif was suggested to be a determinant
... f the target specificity of neurotoxins. Antibodies raised against this motif cross-react among VAMP, SNAP-25, and syntaxin and inhibit the proteolytic activity of the neurotoxins. Moreover, the various neurotoxins cross-inhibit each other's proteolytic action. The role of the three negatively charged residues of the motif in neurotoxin recognition was probed by sitedirected mutagenesis. Substitution of acidic residues in both copies of the VAMP motif indicate that the first one is involved in tetanus neurotoxin recognition, whereas the second one is implicated in binding botulinum B and G neurotoxins. These results suggest that the two copies of the motif have a tandem association in the VAMP molecule. Tetanus neurotoxin (TeNT) 1 and botulinum neurotoxins (BoNTs, seven types from A to G) are three-domain protein toxins that bind selectively to the neuronal presynaptic membrane. They are internalized inside intracellular compartments from which the amino-terminal 50-kDa domain (termed L chain) enters into the cytosol (1-4) . The L chains of TeNT and BoNTs are zinc-endopeptidases that cleave specifically three proteins of the neuroexocytosis apparatus, thereby blocking neurotransmitter release (4 -7). TeNT and BoNT/B, BoNT/D, BoNT/F, and BoNT/G recognize and cleave specifically a synaptic vesicle-associated membrane protein (VAMP, also referred to as synaptobrevin) at different single peptide bonds (4, 8 -12). BoNT/A and BoNT/E specifically recognize and cut The abbreviations used are: TeNT, tetanus neurotoxin; GST, glutathione S-methyl transferase; BoNT, botulinum neurotoxin; VAMP, vesicle-associated membrane protein; VAMP-2, VAMP isoform 2; SNAP-25, synaptosomal-associated protein of 25 kDa; SNARE, soluble N-ethylmaleimide-sensitive factor accessory protein receptor.