The Structural Loop II of Cobrotoxin Is the Main Binding Region for nAChR and Epitope in the Region Is Conformation-Dependent

Abstract

Modification of positively charged residues, Lys and Arg, in cobrotoxin revealed that Lys-27, Lys-47, Arg-28, Arg-30, Arg-33, and Arg-36 of cobrotoxin were essential for the lethality and binding activity to nicotinic acetylcholine receptor (nAChR). The antigenicity of cobrotoxin was drastically diminished when Lys-47, Arg-28, Arg-30, Arg-33, and Arg-36 were modified, while that of the Lys-27-modified derivative was not significantly changed. The CD spectra of cobrotoxin displayed similar patterns after modification of Lys-27, Lys-47, and Arg-28. These findings suggest that Lys-27, Lys-47, and Arg-28 residues may be related to the direct binding to nAChR, and that there is no involvement of Lys-27 in the antigenic determinants of cobrotoxin. Extending the modification to Arg-30, Arg-33, and Arg-36 caused progressive conformational changes of cobrotoxin and resulted in decreased binding activity to antibody and nAChR. This indicates that Arg-30, Arg-33, and Arg-36 may be of structural importance for maintaining the active conformation of cobrotoxin. These results, together with the facts that Tyr-25, Tyr-35, and Trp-29 of cobrotoxin are important in nAChR binding activity, but Trp-29 and Tyr-35 residues are not essential for the antigenicity, suggest that the structural loop II of cobrotoxin is the main binding region for nAChR and the epitope in that region is conformation-dependent.

Cobrotoxin could be an effective therapeutic for COVID-19

“…Cobrotoxin comprises 62 amino acid residues with a molecular weight of about 7 kDa. Cobrotoxin can bind to several subtypes of the nicotinic acetylcholine receptors (nAChRs) and also a few other receptors and ion channels [ 2 ]. The wide distribution of nAChRs may be the main cause of the multiple pharmacodynamic actions of NNAV and cobrotoxin, including analgesic, antiviral, anti-inflammatory, immunoregulatory, and antitumor activities.…”

COVID-19 and pulmonary fibrosis: therapeutics in clinical trials, repurposing, and potential development

“…Cobra venom and NNAV Cobrotoxin and α-neurotoxin from Naja naja atra venom (NNAV) can be used to prevent and relieve symptoms of COVID-19. Cobrotoxin and α-neurotoxin have many pharmacodynamic actions through their binding to nicotinic acetylcholine receptors, which are widely distributed throughout the body (Kuo et al 1995;Lin et al 2020). NNAV and α-neurotoxins can inhibit the cytokine storm through their strong inhibitory effects on inflammation (Lin et al 2020;.…”

Transcriptomic, proteomic, and biochemical analyses reveal a novel neuritogenesis mechanism of Naja naja venom α‐elapitoxin post binding to TrkA receptor of rat pheochromocytoma cells

“…Various studies have reported that long and short-chain postsynaptic neurotoxins adapt a similar folding pattern, consisting of 3 loops-loop 1, loop 2 and loop 3 (Kuo, Chang, & Chang, 1995). The detailed molecular interaction studies on nAChR-binding to neurotoxin have indicated the active participation of several residues, Ser23, Tyr25, Lys27, Trp29, Gln28, Arg43, Gly44, and Lys47, which are of prime functional importance (Kuo et al, 1995). Whereas, in the present study, by alanine scanning mutagenesis and in silico interactive study the active residues involved TA B L E 7 Data showing the percent inhibition of neuritogenesis in PC-12 by signaling pathway(s)-specific small synthetic inhibitors Note: The neuritogenesis induced by Nn-α-elapitoxin-1 in PC-12 cell was considered as 100% activity and other values were compared to that.…”

“…in the interaction between neurotoxin (Nn-α-elapitoxin-1) and TrkA are Asp53, Ser31, Lys69, Gly51, and Lys49 residues (shown in Figure S9), and these are found to be different form the residues of the neurotoxin interacting with nAChR (Kuo et al, 1995). Furthermore, the binding site hotspot residues taking part in an interaction between the neurotoxin and TrkA receptor and thus providing a conducive environment for ligand-receptor interaction dictated by in silico alanine scanning have revealed the key amino acid residues which are of great importance for its functional activity.…”