Binding of Botulinum and Tetanus Neurotoxins to Ganglioside GT1b and Derivatives Thereof

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Abstract
The ability of fragments derived from botulinum neurotoxin (BTx) serotype A to bind to GT1b-coated plastic wells was investigated and compared with the binding characteristics of the parent approximately 150-kDa protein. Although the approximately 50-kDa light chain of BTxA had a marginal binding capacity, the predominant adherence to GT1b-coated wells was exhibited by the approximately 50-kDa carboxy-terminal half of the approximately 100-kDa heavy chain of BTxA; the amino-terminal half of the heavy chain lacked the ability to bind. Binding to GT1b by BTxA and its fragments was compared with that of tetanus neurotoxin (TTx) and the carboxy-terminal half of its heavy chain. Binding of BTxA and the C-terminal half of the heavy chain was optimal in buffers of low ionic strength (mu less than or equal to 0.04 and 0.06, respectively), whereas the heavy chain bound GT1b best at mu greater than or equal to 0.10. TTx and the approximately 50-kDa C-terminal half of its approximately 100-kDa heavy chain bound GT1b at ionic strengths similar to those of BTxA. Comparison of the binding of BTx serotypes A, B, and E to GT1b (using conditions that were found to be optimal for binding by BTxA) indicated differences in the interaction of the three serotypes with GT1b. Compared with BTxA, adherence to GT1b by serotypes B and E was reduced by approximately 60 and approximately 90%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)