Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia.
Illawarra Health and Medical Research Institute (IHMRI), The University of Wollongong, Wollongong, New South Wales 2522, Australia.
Biochem Pharmacol. 2018 Sep;155:288-297. doi: 10.1016/j.bcp.2018.07.007. Epub 2018 Jul 21.
The ribbon isomer of α-conotoxin AuIB has 10-fold greater potency than the wild-type globular isomer at inhibiting nicotinic acetylcholine receptors (nAChRs) in rat parasympathetic neurons, and unlike its globular isoform, ribbon AuIB only targets a specific stoichiometry of the α3β4 nAChR subtype. Previous electrophysiological recordings of AuIB indicated that ribbon AuIB binds to the α3(+)α3(-) interface within the nAChR extracellular domain, which is displayed by the (α3)(β4) stoichiometry but not by (α3)(β4). This specificity for a particular stoichiometry is remarkable and suggests that ribbon isoforms of α-conotoxins might have great potential in drug design. In this study, we investigated the binding mode and structure-activity relationships of ribbon AuIB using a combination of molecular modeling and electrophysiology recording to determine the features that underpin its selectivity. An alanine scan showed that positions 4 and 9 of ribbon AuIB are the main determinants of the interaction with (α3)(β4) nAChR. Our computational models indicate that the first loop of ribbon AuIB binds in the "aromatic box" of the acetylcholine orthosteric binding site, similar to that of globular AuIB. In contrast, the second loop and the termini of the ribbon isomer have different orientations and interactions in the binding sites to those of the globular isomer. The structure-activity relationships reported herein should be useful to design peptides displaying a ribbon α-conotoxin scaffold for inhibition of nAChR subtypes that have hitherto been difficult to selectively target.
α-芋螺毒素 AuIB 的带状异构体对烟碱型乙酰胆碱受体（nAChRs）的抑制作用比野生型球状异构体强 10 倍，与球状异构体不同，带状 AuIB 仅针对特定的α3β4 nAChR 亚基的化学计量。先前对 AuIB 的电生理记录表明，带状 AuIB 结合到 nAChR 细胞外结构域内的α3(+)α3(-)界面，这由（α3）（β4）化学计量显示，但不由（α3）（β4）显示。这种对特定化学计量的特异性非常显著，表明α-芋螺毒素的带状异构体在药物设计中可能具有巨大的潜力。在这项研究中，我们使用分子建模和电生理记录相结合的方法研究了带状 AuIB 的结合模式和结构-活性关系，以确定其选择性的基础特征。丙氨酸扫描表明，带状 AuIB 的 4 位和 9 位是与（α3）（β4）nAChR 相互作用的主要决定因素。我们的计算模型表明，带状 AuIB 的第一个环结合在乙酰胆碱正位结合位点的“芳香盒”中，类似于球状 AuIB。相比之下，第二个环和带状异构体的末端在结合位点与球状异构体的取向和相互作用不同。本文报道的结构-活性关系对于设计显示带状α-芋螺毒素支架的肽以抑制迄今为止难以选择性靶向的 nAChR 亚型应该是有用的。
