A New Peptide from the Venom of the Madagascar Cat-Eyed Snake Madagascarophis colubrinus Blocks Nicotinic Acetylcholine Receptor

— In screening the venoms of various snake species, we found that the venom of the Madagascar cat-eyed snake Madagascarophis colubrinus competes with α-bungarotoxin for binding to the nicotinic acetylcholine receptor from Torpedo californica . Using liquid chromatography, a peptide that inhibits the binding of α‑bungartoxin to this receptor was isolated from the venom and named macoluxin. The amino acid sequence of this 23-amino acid peptide was determined by automatic Edman degradation. Comparison with amino acid sequences of known proteins showed that the macoluxin sequence is homologous to the α-helical region of the sequence of snake venom metalloproteinases. The peptide was synthesized by solid-phase peptide synthesis, and the study of its biological activity showed that it inhibits the binding of α-bungarotoxin to the Torpedo receptor with an IC 50 of 47 μM. Macoluxin also reversibly inhibited acetylcholine-induced currents in the muscle-type nicotinic acetylcholine receptor. This is the first data on the presence of a peptide that can inhibit the nicotinic acetylcholine receptor in the venom of rear-fanged snakes.