Toxin Evolution Lab, University of Queensland, Biological Sciences, St. Lucia, QLD 4072, Australia.
Department of Pharmacology, Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia.
Int J Mol Sci. 2020 Oct 6;21(19):7377. doi: 10.3390/ijms21197377.
The evolution of an aquatic lifestyle from land dwelling venomous elapids is a radical ecological modification, bringing about many evolutionary changes from morphology to diet. Diet is an important ecological facet which can play a key role in regulating functional traits such as venom composition and prey-specific targeting of venom. In addition to predating upon novel prey (e.g., fish, fish eggs and invertebrates), the venoms of aquatic elapids also face the challenge of increased prey-escape potential in the aquatic environment. Thus, despite the independent radiation into an aquatic niche on four separate occasions, the venoms of aquatic elapids are evolving under convergent selection pressures. Utilising a biolayer interferometry binding assay, this study set out to elucidate whether crude venoms from representative aquatic elapids were target-specific to the orthosteric site of postsynaptic nicotinic acetylcholine receptor mimotopes of fish compared to other terrestrial prey types. Representatives of the four aquatic lineages were: aquatic coral snakes representative was ;, sea kraits representative was sea snakes representatives were two spp. and eight spp; and water cobras representative was . No prey-specific differences in crude venom binding were observed from any species tested, except for which showed slight evidence of prey-potency differences. For , , and , there was a lack of binding to the orthosteric site of any target lineage. Subsequent testing on the in vitro chick-biventer cervicis muscle preparation suggested that, while the venoms of these species bound postsynaptically, they bound to allosteric sites rather than orthosteric. Allosteric binding is potentially a weaker but faster-acting form of neurotoxicity and we hypothesise that the switch to allosteric binding is likely due to selection pressures related to prey-escape potential. This research has potentially opened up the possibility of a new functional class of toxins which have never been assessed previously while shedding light on the selection pressures shaping venom evolution.
水生生活方式是从陆生毒蛇进化而来的，这是一种激进的生态改变，从形态到饮食带来了许多进化上的变化。饮食是一个重要的生态方面，它可以在调节毒液成分和毒液对特定猎物的靶向等功能特征方面发挥关键作用。除了捕食新的猎物（例如鱼类、鱼卵和无脊椎动物）之外，水生蛇类的毒液还面临着在水生环境中增加猎物逃避能力的挑战。因此，尽管水生蛇类已经独立地辐射到四个不同的生态位，但它们的毒液正在受到趋同选择压力的影响。本研究利用生物层干涉法结合测定，旨在阐明代表水生蛇类的粗毒液是否对鱼类烟碱型乙酰胆碱受体模拟肽的正构位点具有特异性，而不是对其他陆地猎物类型具有特异性。选择了四个水生谱系的代表：水生珊瑚蛇的代表是 ；海蝰的代表是 ；海蛇的代表是两个 种和八个 种；水蚺的代表是 。除了 种显示出轻微的猎物效力差异外，从任何测试的物种中都没有观察到粗毒液结合的猎物特异性差异。对于 、 、 、 和 ，没有针对任何目标谱系的正位点结合。随后在体外小鸡双颈肌准备物上的测试表明，尽管这些物种的毒液结合在突触后，但它们结合的是变构部位而不是正位点。变构结合可能是一种较弱但作用更快的神经毒性形式，我们假设向变构结合的转变可能是由于与猎物逃避潜力相关的选择压力所致。这项研究有可能开辟了一个新的功能类毒素的可能性，这些毒素以前从未被评估过，同时也揭示了塑造毒液进化的选择压力。
