Novel Three-Finger Neurotoxins from Naja melanoleuca Cobra Venom Interact with GABA(A) and Nicotinic Acetylcholine Receptors

Cobra venoms contain three-finger toxins (TFT) including α-neurotoxins efficiently binding nicotinic acetylcholine receptors (nAChRs). As shown recently, several TFTs block GABA(A) receptors (GABA(A)Rs) with different efficacy, an important role of the TFTs central loop in binding to these receptors being demonstrated. We supposed that the positive charge (Arg36) in this loop of α-cobratoxin may explain its high affinity to GABA(A)R and here studied α-neurotoxins from African cobra N. melanoleuca venom for their ability to interact with GABAARs and nAChRs. Three α-neurotoxins, close homologues of the known N. melanoleuca long neurotoxins 1 and 2, were isolated and sequenced. Their analysis on Torpedo californica and α7 nAChRs, as well as on acetylcholine binding proteins and on several subtypes of GABA(A)Rs, showed that all toxins interacted with the GABA(A)R much weaker than with the nAChR: one neurotoxin was almost as active as α-cobratoxin, while others manifested lower activity. The earlier hypothesis about the essential role of Arg36 as the determinant of high affinity to GABA(A)R was not confirmed, but the results obtained suggest that the toxin loop III may contribute to the efficient interaction of some long-chain neurotoxins with GABA(A)R. One of isolated toxins manifested different affinity to two binding sites on Torpedo nAChR.