Toxin Evolution Lab, School of Biological Sciences, University of Queensland, St Lucia, QLD 4072, Australia.
Universeum, Södra Vägen 50, 412 54 Gothenburg, Sweden.
Comp Biochem Physiol C Toxicol Pharmacol. 2021 Feb;240:108921. doi: 10.1016/j.cbpc.2020.108921. Epub 2020 Oct 26.
Bitis are well known for being some of the most commonly encountered and medically important snake species in all of Africa. While the majority of species possess potently anticoagulant venom, only B. worthingtoni is known to possess procoagulant venom. Although known to be the basal species within the genus, B. worthingtoni is an almost completely unstudied species with even basic dietary information lacking. This study investigated various aspects of the unique procoagulant effects of B. worthingtoni venom. Coagulation assays determined the primary procoagulant effect to be driven by Factor X activating snake venom metalloprotease toxins. In addition to acting upon the mammalian blood clotting cascade, B. worthingtoni venom was also shown to clot amphibian plasma. As previous studies have shown differences in clotting factors between amphibian and mammalian plasmas, individual enzymes in snake venoms acting on plasma clotting factors can be taxon-selective. As venoms evolve under purifying selection pressures, this suggests that the procoagulant snake venom metalloprotease toxins present in B. worthingtoni have likely been retained from a recent common ancestor shared with the related amphibian-feeding Proatheris superciliaris, and that both amphibians and mammals represent a substantial proportion of B. worthingtoni current diet. Thus, taxon-specific actions of venoms may have utility in inferring dietary composition for rare or difficult to study species. An important caveat is that to validate this hypothesis field studies investigating the dietary ecology of B. worthingtoni must be conducted, as well as further investigations of its venom composition to reconstruct the molecular evolutionary history of the toxins present.
角蝰属是在整个非洲最常见和最重要的医学蛇种之一。虽然大多数物种都具有强大的抗凝毒液，但只有沃氏角蝰被认为具有促凝血毒液。尽管沃氏角蝰被认为是该属的基础物种，但它是一种几乎完全未被研究的物种，甚至缺乏基本的饮食信息。本研究调查了沃氏角蝰毒液独特促凝血作用的各个方面。凝血测定确定了主要的促凝血作用是由激活因子 X 的蛇毒金属蛋白酶毒素驱动的。除了作用于哺乳动物凝血级联反应外，沃氏角蝰毒液还能使两栖动物血浆凝固。由于先前的研究表明两栖动物和哺乳动物血浆中的凝血因子存在差异，蛇毒液中作用于血浆凝血因子的单个酶可以是分类选择性的。由于毒液在净化选择压力下进化，这表明沃氏角蝰中存在的促凝血蛇毒金属蛋白酶毒素可能是从与其相关的以两栖动物为食的拟角蝰中最近的共同祖先中保留下来的，并且两栖动物和哺乳动物都代表了沃氏角蝰当前饮食的重要组成部分。因此，毒液的分类特异性作用可能有助于推断稀有或难以研究物种的饮食成分。一个重要的警告是，为了验证这一假设，必须进行沃氏角蝰饮食生态学的实地研究，以及对其毒液成分的进一步研究，以重建存在毒素的分子进化历史。
