Purification and sequence determination of a new muscarinic toxin (MT4) from the venom of the green mamba (Dendroaspis angusticeps).

A. Vandermeers, M.-C. Vandermeers-Piret, J. Rathe, M. Waelbroeck, M. Jolkkonen, A. Oras and E. Karlsson. Purification and sequence determination of a new muscarinic toxin (MT4) from the venom of the green mamba (Dendroaspis angusticeps). Toxicon 33, 1171-1179, 1995.-A toxin which partially inhibited [ 3 H]N-methylscopolamine binding to rat brain muscarinic receptors was purified from the venom of green mamba, Dendroaspis angusticeps. The N-terminal sequence (up to 45 amino acids) was determined by automated Edman degradation of the whole molecule. The complete sequence was elucidated after enzymatic cleavage with endoproteinase Arg-C or endoproteinase Lys-C and peptide fragments purification. The identity of the C-terminal amino acid was confirmed by hydrazinolysis. The new toxin (MT4) had eight half-cystines and 66 amino acids. It differed from muscarinic toxin MT1 by a single substitution in position 57 (arginine in MT1, histidine in MT4), proximal to the sixth half-cystine.