Snake Venomics of the Arboreal Talamancan Palm-Pitviper, Bothriechis nubestris, Provides Clues on the Origin of a Phenotypic Dichotomy between Type-I and Type-II Venoms

Abstract

We report the biochemical and proteomic characterizationof the venom of the arboreal Talamancan palm-pitviper,Bothriechis nubestris, a species endemic to north and central parts ofthe Costa Rican Cordillera de Talamanca, at 2100 to 3000 m abovesea level. The Talamancan palm-pitviper venom arsenal comprisedthe translated products of 26 unique transcripts into 10 toxinclasses, where metalloproteinases PIIa and PIII represent thedominant components. In vitro, the venom proteolyzed azocaseinand gelatin but showed no phospholipase A2 or human plasmacoagulant activities. In vivo, B. nubestris venom exhibited anintravenous median lethal dose (LD50) of 21.5 (95% confidenceinterval: 15.6−29.5) μg/mouse, and a minimum hemorrhagic dose(MHD) of 1.85 μg. PoliVal-ICP antivenom neutralized the venom’s lethal activity with a potency of 9.7 mg of venom/g ofantivenom and significantly reduced the hemorrhagic effect. Comparison of venom gland transcriptomes and venom proteomes of B.nubestris and its closest congeneric relative, B. nigroviridis, revealed that highly conserved venom gland transcriptomes aredifferentially processed by each species to produce divergent (type-I vs type-II, respectively) venoms. This phenomenon contributesto the remarkable venom phenotypic variability found across the palm-pitviper phylogeny. A possible mechanism for the occurrenceof type-I/type-II venom phenotypic dichotomy is discussed.