Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, New South Wales, Australia.
Institute for Molecular Bioscience, Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science, The University of Queensland, Brisbane, Queensland, Australia.
J Neurochem. 2022 Jan;160(2):154-171. doi: 10.1111/jnc.15535. Epub 2021 Nov 15.
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 GABA receptors (GABA R) inhibiting HVA N-type calcium (Cav2.2) channels and reducing membrane excitability in mouse DRG neurons. The inhibition of HVA Ba currents and neuroexcitability by GeXIVA[1,3] was partially reversed by the selective GABA R antagonist CGP 55845. In transfected HEK293T cells co-expressing human GABA R1 and R2 subunits and Cav2.2 channels, both GeXIVA[1,3] and GeXIVA[1,4] inhibited depolarization-activated Ba 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 GABA R-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 GABA R in HEK293T cells. This study highlights GABA R as a potentially important receptor target for the activity of αO-conotoxin GeXIVA to mediate analgesia.
αO-Conotoxin GeXIVA 是一种 28 个氨基酸的肽，来源于海洋蜗牛 Conus generalis 的毒液。GeXIVA 结构中存在四个半胱氨酸残基，因此它有三种不同的二硫键异构体，即球形、带状或珠状异构体。所有三种异构体都在 α9α10 烟碱型乙酰胆碱受体上具有活性，珠状异构体 GeXIVA[1,2] 的活性最强，并在神经性疼痛的动物模型中表现出镇痛活性。最初报道 GeXIVA 的活性时，未能观察到异构体对大鼠背根神经节 (DRG) 神经元中的高电压激活 (HVA) 钙通道电流有任何影响。在这项研究中，我们首次报道了球形 GeXIVA[1,3] 对 G 蛋白偶联 GABA 受体 (GABA R) 的活性，该活性可抑制 HVA N 型钙 (Cav2.2) 通道并降低小鼠 DRG 神经元的膜兴奋性。GABA R 选择性拮抗剂 CGP 55845 部分逆转了 GeXIVA[1,3] 对 HVA Ba 电流和神经兴奋性的抑制作用。在共表达人 GABA R1 和 R2 亚基和 Cav2.2 通道的转染 HEK293T 细胞中，GeXIVA[1,3] 和 GeXIVA[1,4] 均抑制了由 Cav2.2 通道介导的去极化激活的 Ba 电流，而 GeXIVA[1,2] 则没有作用。还测试了三种环化 GeXIVA[1,4] 带状异构体的作用，其中 cGeXIVA GAG 对人 GABA R 偶联的 Cav2.2 通道最为有效。有趣的是，球形 GeXIVA[1,3] 还可逆地增强了共表达与 GABA R 的人 GIRK1/2 通道介导的内向整流 K 电流。这项研究强调了 GABA R 作为 αO-Conotoxin GeXIVA 发挥镇痛作用的潜在重要受体靶点。
