Botulinum neurotoxin interactions with substrate

Abstract

The mechanism by which a CNT properly identifies and cleaves its target SNARE once inside the neuron involves one or more regions of enzyme–substrate interaction remote from the active site (so called exosites). We determined the structure of a CNT endopeptidase in complex with its target SNARE that illustrates the extensive enzyme–substrate interface and the basis of substrate selectivity. Our structure of BoNT/A, in complex with human SNAP-25, revealed multiple exosites, including several that are involved in substrate specificity, and one that likely functions as an allosteric activator of the toxin. Different crystal forms of wildtype BoNT/A revealed conformational variability of several loops near the active site. We also determined crystal structures of the apo form of the TeNT LC49 and that of the BoNT/C1 LC protease50. We found remarkable structural differences between the BoNT/C1 and BoNT/A LC proteases that may explain the dual substrate-binding ability of BoNT/C1.