Interaction of modified neurotoxins from Naja nigricollis with the nicotinic acetylcholine receptor from Torpedo marmorata A Raman spectroscopy study

Two derivatives of α-toxin from Naja nigricollis venom were used in order to study, by resonance Raman spectroscopy, its interaction with the nicotinic acetylcholine (AcCho) receptor from membranes of Torpedo marmorata electrocytes. The two modified toxins carry either an NO₂ group bound to Tyr²⁵ or a nitrophenylthioether (NPS) bound to Trp²⁵. The comparison of the spectra of the free and bound derivatized toxins indicates that the environment of Tyr²⁵ is not perturbed upon binding to the AcCho receptor, but the surroundings of NPS bound to Trp²⁹ are changed. This result indicates that Tyr²⁵ is not involved in binding, while Trp²⁹ of the α-toxin may be in contact with the AcCho receptor. Examination of the spectrum of the AcCho receptor membrane after binding of the NPS-Trp toxin discloses some modifications of the vibrations of the tryptophan and cysteine disulfide bridge of the receptor. These residues are possibly involved in toxin binding.