ELECTRON-DENSITY PROJECTION MAP OF THE BOTULINUM NEUROTOXIN 900-KILODALTON COMPLEX BY ELECTRON CRYSTALLOGRAPHY

The 900-kDa botulinum neurotoxin complex serotype A has been crystalli zed by the lipid-layer two-dimensional crystallization technique. Base d on the binding characteristics of the hemagglutinating portion of th e complex, a number of ganglioside/ lipid mixtures were tested but onl y lactosyl ceramide/1- -palmityl-2-oleoyl-sn-glycero-3-phosphocholine was found to crystallize the complex. The optimum lipid mixture contai ned 75 mass % lactosyl ceramide and 25 mass % 1-palmityl-2-oleoyl-sn-g lycero-3-phosphocholine. Using protein concentrations from 5 to 500 mu g/ml and pH 5 acetate buffer, we have obtained crystals that diffract to better than 15 Angstrom when prepared in negative stain,A projecti on map with a resolution of 30 Angstrom was calculated with unit cell dimensions of a = b = 157 Angstrom and P3 symmetry. The complex is tri angular in shape with six distinct lobes observed, Additionally, six s maller structures protrude from the triangular core. (C) 1997 Academic Press.