An environmentally sustainable production platform for a variety of correctly folded cyclic disulfide-rich peptides with enhanced yields.

Background and Purpose: Activation of GIRK channels via G protein-coupled GABA B receptors has been shown to attenuate nociceptive transmission. The analgesic α-conotoxin Vc1.1 activates GABA B receptors resulting in inhibition of Ca v 2.2 and Ca v 2.3 channels in mammalian primary afferent neurons. Here, we investigated the effects of analgesic α-conotoxins on recombinant and native GIRK-mediated K + currents and on neuronal excitability.Experimental Approach: The effects of analgesic α-conotoxins, Vc1.1, RgIA, and PeIA, were investigated on inwardly-rectifying K + currents in HEK293T cells recombinantly co-expressing either heteromeric human GIRK1/2 or homomeric GIRK2 subunits, with GABA B receptors. The effects of α-conotoxin Vc1.1 and baclofen were studied on GIRK-mediated K + currents and the passive and active electrical properties of adult mouse dorsal root ganglion neurons. Key Results: Analgesic α-conotoxins Vc1.1, RgIA, and PeIA potentiate inwardly-rectifying K + currents in HEK293T cells recombinantly expressing human GIRK1/2 channels and GABA B receptors. GABA B receptor-dependent GIRK channel potentiation by Vc1.1 and baclofen occurs via a pertussis toxin-sensitive G protein and is inhibited by the selective GABA B receptor antagonist CGP 55845. In adult mouse dorsal root ganglion neurons, GABA B receptor-dependent GIRK channel potentiation by Vc1.1 and baclofen hyperpolarizes the cell membrane potential and reduces excitability. Conclusions and Implications: This is the first report of GIRK channel potentiation via allosteric α-conotoxin Vc1.1-GABA B receptor agonism, leading to decreased neuronal excitability. Such action potentially contributes to the analgesic effects of Vc1.1 and baclofen observed in vivo.

αO‐Conotoxin GeXIVA is a 28 amino acid peptide derived from the venom of the marine snail Conus generalis. The presence of four cysteine residues in the structure of GeXIVA allows it to have three different disulfide isomers, that is, the globular, ribbon or bead isomer. All three isomers are active at α9α10 nicotinic acetylcholine receptors, with the bead isomer, GeXIVA[1,2], being the most potent and exhibiting analgesic activity in animal models of neuropathic pain. The original report of GeXIVA activity failed to observe any effect of the isomers on high voltage‐activated (HVA) calcium channel currents in rat dorsal root ganglion (DRG) neurons. In this study, we report, for the first time, the activity of globular GeXIVA[1,3] at G protein‐coupled GABAB receptors (GABABR) inhibiting HVA N‐type calcium (Cav2.2) channels and reducing membrane excitability in mouse DRG neurons. The inhibition of HVA Ba2+ currents and neuroexcitability by GeXIVA[1,3] was partially reversed by the selective GABABR antagonist CGP 55845. In transfected HEK293T cells co‐expressing human GABABR1 and R2 subunits and Cav2.2 channels, both GeXIVA[1,3] and GeXIVA[1,4] inhibited depolarization‐activated Ba2+ currents mediated by Cav2.2 channels, whereas GeXIVA[1,2] had no effect. The effects of three cyclized GeXIVA[1,4] ribbon isomers were also tested, with cGeXIVA GAG being the most potent at human GABABR‐coupled Cav2.2 channels. Interestingly, globular GeXIVA[1,3] also reversibly potentiated inwardly‐rectifying K+ currents mediated by human GIRK1/2 channels co‐expressed with GABABR in HEK293T cells. This study highlights GABABR as a potentially important receptor target for the activity of αO‐conotoxin GeXIVA to mediate analgesia.