Structure-Activity Studies Reveal the Molecular Basis for GABA(B)-Receptor Mediated Inhibition of High Voltage-Activated Calcium Channels by α-Conotoxin Vc1.1

Authors

Mahsa Sadeghi, University of WollongongFollow
Bodil B. Carstens, University of Queensland
Brid P. Callaghan, University of Wollongong, University of Queensland
James T. Daniel, University of Queensland
Han Shen Tae, University of WollongongFollow
Tracey O'Donnell, Flinders University, University of Adelaide
Joel Castro, University of Adelaide, Flinders University
Stuart Brierley, Flinders University, University of AdelaideFollow
David J. Adams, University of WollongongFollow
David J. Craik, University of Queensland
Richard J. Clark, University of QueenslandFollow

RIS ID

128552

Publication Details

Sadeghi, M., Carstens, B. B., Callaghan, B. P., Daniel, J. T., Tae, H., O'Donnell, T., Castro, J., Brierley, S. M., Adams, D. J., Craik, D. J. & Clark, R. J. (2018). Structure-Activity Studies Reveal the Molecular Basis for GABA(B)-Receptor Mediated Inhibition of High Voltage-Activated Calcium Channels by α-Conotoxin Vc1.1. ACS Chemical Biology, 13 (6), 1577-1587.

Abstract

α-Conotoxins are disulfide-bonded peptides from cone snail venoms and are characterized by their affinity for nicotinic acetylcholine receptors (nAChR). Several α-conotoxins with distinct selectivity for nAChR subtypes have been identified as potent analgesics in animal models of chronic pain. However, a number of α-conotoxins have been shown to inhibit N-type calcium channel currents in rodent dissociated dorsal root ganglion (DRG) neurons via activation of G protein-coupled GABA_B receptors (GABA_BR). Therefore, it is unclear whether activation of GABA_BR or inhibition of α9α10 nAChRs is the analgesic mechanism. To investigate the mechanisms by which α-conotoxins provide analgesia, we synthesized a suite of Vc1.1 analogues where all residues, except the conserved cysteines, in Vc1.1 were individually replaced by alanine (A), lysine (K), and aspartic acid (D). Our results show that the amino acids in the first loop play an important role in binding of the peptide to the receptor, whereas those in the second loop play an important role for the selectivity of the peptide for the GABA_BR over α9α10 nAChRs. We designed a cVc1.1 analogue that is >8000-fold selective for GABA_BR-mediated inhibition of high voltage-activated (HVA) calcium channels over α9α10 nAChRs and show that it is analgesic in a mouse model of chronic visceral hypersensitivity (CVH). cVc1.1[D11A,E14A] caused dose-dependent inhibition of colonic nociceptors with greater efficacy in ex vivo CVH colonic nociceptors relative to healthy colonic nociceptors. These findings suggest that selectively targeting GABA_BR-mediated HVA calcium channel inhibition by α-conotoxins could be effective for the treatment of chronic visceral pain.

Grant Number

NHMRC/1049928