Unique Pharmacological Properties of α-Conotoxin OmIA at α7 nAChRs

Abstract

OmIA, isolated from Conus omaria venom, is a potent antagonist at α7 nAChRs. We determined the co-crystal structure of OmIA with Lymnae stagnalis acetylcholine binding protein (Ls-AChBP) that identified His5, Val10 and Asn11 as key determinants for the high potency of OmIA at α7 nAChRs. Remarkably, despite a competitive binding mode observed in the co-crystal structure, OmIA and analogues displayed functional insurmountable antagonism at α7 and α3β4 nAChRs, except OmIA analogues having long side chain at position 10 ([V10Q]OmIA and [V10L]OmIA), which were partial insurmountable antagonist at α7 nAChRs in the presence of type II positive allosteric modulators (PAMs). A “two-state, two-step” model was used to explain these observations, with [V10Q]OmIA and [V10L]OmIA co-existing in a fast reversible/surmountable as well as a tight binding/insurmountable state. OmIA and analogues also showed biphasic-inhibition at α7 nAChRs in the presence of PNU120596, with a preference for the high-affinity binding site following prolonged exposure. The molecular basis of binding and complex pharmacological profile of OmIA at α7 nAChRs presented in here expands on the potential of α-conotoxins to probe the pharmacological properties of nAChRs and may help guide the development novel α7 modulators.

Unravelling the allosteric binding mode of αD-VxXXB at nicotinic acetylcholine receptors

“…Based on previous experimental determinations ( Abraham et al, 2017 ; Ho et al, 2021a ; Ho et al, 2021b ), purified de-tagged Ls -AChBP and synthesized VxXXB-C(21–50) were mixed at a molar ratio of 1:2 at 4°C for 1 h before setting up crystallization trials. Crystals were successfully grown at room temperature using the hanging drop method by mixing protein and reservoir solution composed of 0.91 M lithium chloride, 16% PEG6000 and 0.1 M MES monohydrate pH 6.4 at a ratio 1:1 v/v.…”

Marine natural products

“…660 A crystal structure of a4/7-conotoxin OmIA (C. omaria) with Lymnae stagnalis acetylcholine binding protein, at 2.47 Å resolution, has identied principal interactions between His5 and Ala7 of the conotoxin with C-loop residues Tyr185-Tyr192 and the conotoxin disulde and Cys188-Cys189. 661 A 26-residue conotoxin belonging to the Asuperfamily, identied from a cDNA library of C. striatus, exhibits in vivo analgesic activity, 662 Syntheses of ascidian metabolites 19-bromoisoeudistomin U, 672 ritterazine B, 673 (−)-rossinone A, 674 (−)-herdmanine D 675 and siladenoserinol D 676 have been reported. Examination of the cellular effects of synthetic biselide A using image-based phenotypic screening identied that the macrolide can be added to the growing list of MNPs that target microtubules and microtubule dependent structures.…”

“…660 A crystal structure of α4/7-conotoxin OmIA ( C. omaria ) with Lymnae stagnalis acetylcholine binding protein, at 2.47 Å resolution, has identified principal interactions between His5 and Ala7 of the conotoxin with C-loop residues Tyr185–Tyr192 and the conotoxin disulfide and Cys188–Cys189. 661 A 26-residue conotoxin belonging to the A-superfamily, identified from a cDNA library of C. striatus , exhibits in vivo analgesic activity, 662 while synthetic cal14.2b ( Californiconus californicus ) exhibited insulinotropic activities in vitro and in vivo suggesting potential roles in the treatment of Type 2 diabetes. 663 ω-Conotoxins characteristically inhibit N -type voltage-gated calcium channels and in the specific case of ω-conotoxin MVIIA, have application in the treatment of neuropathic pain.…”

Efficient Expression in Leishmania tarentolae (LEXSY) of the Receptor-Binding Domain of the SARS-CoV-2 S-Protein and the Acetylcholine-Binding Protein from Lymnaea stagnalis

“…Several AChBPs were discovered to date in various mollusks [ 12 , 13 , 14 ] and some other invertebrates, e.g., spider Pardosa pseudoannulata [ 15 ]. Two representatives (from Lymnaea stagnalis and Aplisia californica mollusks) are most often used in scientific research either in the form of wild-type protein (see, for example, [ 16 , 17 , 18 ]) or after extensive mutagenesis [ 19 , 20 ]. Spider AChBP is considered to be a close structural mimic of the insect nAChRs, which can be used in crop protection-related research [ 15 ] complementing the use of Lymnaea stagnalis AChBP Q55R point mutant for the structural studies of insecticides [ 21 ].…”