Abstract
Toxin-g, the venom spitted by African spitting cobra, Naja nigricollis nigricollis, could induced a corneal opacity via its binding to corneal GAGs, chondroitin sulfate, leading to opacity or temporary blindness of the victim. In this study heparin, another class of GAG, and chondroitin sulfate-derived disaccharide are investigated by high resolution 1H NMR to seek inside the molecular details of toxin-g--GAG interaction. We performed an NMR structural analysis of the heparin/chondroitin binding site of toxin-g and determined the bound conformation of heparin/chondroitin-derived disaccharide under non-aggregated condition using complete relaxation and conformational exchange matrix analysis (CORCEMA). The result suggest that chondroitin anomeric proton have some influence in the binding affinity of the GAG to toxin-g; it is proved that b-anomer of chondroitin sulfate have a better affinity than a-anomer in binding to toxin-g. The binding of toxin-g to chondroitin induce a conformational change in chondroitin while such a change is not clearly observable in heparin, which bind more weakly to toxin-g. Chondroitin and heparin were also observed to bind in different behaviour to toxin-g, where the heparin—toxin-g binding behaviour was more comparable to heparin-CTX A3 behaviour. The results suggested that chondroitin anomeric proton have some influence in the binding affinity of the GAG to toxin-g; it is proved that b-anomer of chondroitin sulfate has a better affinity than a-anomer in binding to toxin-g. Based on the studies of b-anomer chondroitin sulfate—toxin-g complex, the toxin-g exists two different binding sites.