Erabutoxin b. Structure/function relationships following initial protein refinement at 0.140-nm resolution

A study has been made, following high-resolution refinement at 0.14 nm, of the structure of erabutoxin b, prototype postsynaptic neurotoxin from snake venom. The detailed patterns of intramolecular van der Waal's interactions have been determined. From information, hitherto unavailable, about atomic temperature parameters, the relative mobilities in different regions of the molecule have been estimated. A detailed model of structure/function relationships in these neurotoxins, which bind to the acetylcholine receptor, has thus been established: the probable dynamic mode of toxin-receptor binding is described. The model identifies, and the binding mode depends on a unique structural feature of these protein toxins: the hydrophobic 'Trp' cleft. Charge-charge interactions are implicated in initial toxin orientation on the receptor surface. Possible reactive-site extension in short-chain toxins is described. Modifications in binding mode of long-chain toxins are considered. The relative mobilities of antigenic site residues are discussed.