Cysteine [2,4] Disulfide Bond as a New Modifiable Site of α-Conotoxin TxIB

Abstract

α-Conotoxin TxIB, a selective antagonist of α6/α3β2β3 nicotinic acetylcholine receptor, could be a potential therapeutic agent for addiction and Parkinson’s disease. As a peptide with a complex pharmacophoric conformation, it is important and difficult to find a modifiable site which can be modified effectively and efficiently without activity loss. In this study, three xylene scaffolds were individually reacted with one pair of the cysteine residues ([1,3] or [2,4]), and iodine oxidation was used to form a disulfide bond between the other pair. Overall, six analogs were synthesized with moderate isolated yields from 55% to 65%, which is four times higher than the traditional two-step oxidation with orthogonal protection on cysteines. The cysteine [2,4] modified analogs, with higher stability in human serum than native TxIB, showed obvious inhibitory effect and selectivity on α6/α3β2β3 nicotinic acetylcholine receptors (nAChRs), which was 100 times more than the cysteine [1,3] modified ones. This result demonstrated that the cysteine [2,4] disulfide bond is a new modifiable site of TxIB, and further modification can be a simple and feasible strategy for the exploitation and utilization of α-Conotoxin TxIB in drug discovery.

Marine natural products

“…652 Investigation of engineered variants of α-conotoxin LvIB identified the influence of residues Gln141, Asn184 and Lys186 on α7 nAChR species selectivity. 653 Xylene-linked cysteine [2,4] modified analogues of α-conotoxin TxIB have enhanced serum stability and show selectivity towards α6/α3β2β3 nAChR's 654 while an alkyne variant, replacing cysteine [1,3], of α-conotoxin Vc1.1 failed to inhibit α7 and hα9α10 nAChR's but was a GABA B R selective agonist and also reversed mechanical allodynia in vivo . 655 α-Conotoxins promote the proliferation of C6 glioma cells in vitro .…”

Molecular Determinants of Species Specificity of α-Conotoxin TxIB towards Rat and Human α6/α3β4 Nicotinic Acetylcholine Receptors

“…TxIB, a conotoxin consisting of 16 amino acids found in Conus textiles, specifically blocks rα6/α3β2β3 nAChR, with an IC 50 value of 28 nM. It has no effect on rα6/α3β4 nAChR (IC 50 > 10,000 nM) and is one of the best ligands available that interact with α6/α3β2β3 nAChR [19]. In contrast, when examining the action of TxIB on human nAChRs, it was found to block hα6/α3β4, with an IC 50 value of 537 nM [20,21].…”

α-Conotoxin TxIB Inhibits Development of Morphine-Induced Conditioned Place Preference in Mice via Blocking α6β2* Nicotinic Acetylcholine Receptors

“…α -Conotoxin TxIB is a small peptide with shortcomings such as poor stability, short half-life, and poor bioavailability. In order to improve these, it has been cyclized and structurally modified for future applications ( Li et al, 2020 ; Zhang et al, 2021 ). Previous studies evaluated the anti-nicotine addiction activity of TxIB by establishing a nicotine-induced CPP model, and the results showed that TxIB has obvious inhibitory effect on the establishment and relapse of nicotine-induced CPP ( You et al, 2019 ).…”