Comparison of conformations of Mojave toxin subunits and reconstituted toxin

Abstract

1. 1. Mojave toxin is a presynaptic neurotoxin isolated from the venom of Mojave rattlesnake. It is composed of two subunits, an acidic protein called subunit A and a basic protein, subunit B. The two subunits can combine to form the reconstituted Mojave toxin which possesses full biological activities. 2. 2. Peptide backbone conformations of these subunits and the reconstituted toxin were investigated by Raman spectroscopy and circular dichroism spectroscopy and compared to the native toxin conformation. It was found to consist mainly of an α-helix structure. 3. 3. Quantitative estimation of conformation calculated by the method of Lippert from the Raman spectroscopy gave 71% α-helix, 18% β-sheet and 11% random coil structures for the acidic subunit. 4. 4. Values of 67% α-helix, 16% β-structure and 17% random structure were obtained from data derived from the basic subunit. 5. 5. The values generated from the recombinant toxin were 70% α-helix, 16% β-sheet and 14% random structure. It was found that the conformation of the reconstituted toxin is essentially identical to the native Mojave toxin. 6. 6. Conformation of disulfide bonds and the microenvironment of tyrosine aromatic side chains were also studied by Raman spectroscopy. 7. 7. These studies indicate that when the two subunits combine to form the reconstituted toxin, peptide backbone, disulfide conformations and the microenvironment of tyrosine side chains were largely retained without significant alteration.