METAL SUBSTITUTION OF TETANUS NEUROTOXIN

Tetanus neurotoxin was depleted of its catalytic Zn2+ ion, and the apo toxin was reconstituted with different transition metal ions. The Mn2- and Co2+-tetanus neurotoxins are highly active in the proteolysis of vesicle-associated membrane protein/synaptobrevin, the natural substr ate of this toxin, whereas Cu2+ and Fe2+ minimally supported proteolyt ic activity. The visible absorbance spectrum of Co2+-tetanus neurotoxi n shows an maximum at 538 nm with a molar absorption coefficient of 82 M(-1) . cm(-1). These results indicate that the Zn2+ environment at t he active site of tetanus neurotoxin is different from those of known Zn2+-endopeptidases and provide a structural basis for the definition of tetanus neurotoxin, and the related clostridial neurotoxins, as an independent family of metalloproteases.