Venomics of the Duvernoy's gland secretion of the false coral snake Rhinobothryum bovallii (Andersson, 1916) and assessment of venom lethality towards synapsid and diapsid animal models

Abstract

The Duvernoy's gland secretory proteome of the false coral snake Rhinobothryum bovallii (Costa Rica), unveiled applying bottom-up venomics, comprises a handful of toxins belonging to only three protein families, three-finger toxin (3FTx), cysteine-rich secretory protein (CRISP), and snake venom metalloprotease (PIII-SVMP). Except for small differences in the relative abundance of the PIII-SVMPs, which may be due to individual variability, no evidence of geographic variability or ontogenetic changes was found among the venom proteomes of the juvenile and adult R. bovallii snakes sampled. Major monomeric (86.5%mol) and minor dimeric (2.8%mol) 3FTxs dominate the toxin arsenal of the Costa Rican false coral snake. The remaining 10.7% of the venom proteome comprises CRISP (8.2%) and PIII-SVMP (2.4%) molecules. In vivo lethality assays showed that R. bovallii produces venom that is non-toxic towards mammalian prey, and which exerts a different toxic effect on domestic chicken chicks and baby green iguana. Toxicovenomic analysis of R. bovallii venom in the iguana model identified two 3FTx RP-HPLC fractions that faithfully mimicked the irreversible immobilizing effect of the whole venom. BIOLOGICAL SIGNIFICANCE: With more than 2200 species in family Colubridae (sensu lato), rear-fanged snakes comprise approximately two-thirds of the extant species of advanced snakes. Snakebites from venomous snakes that are of medical concern are predominantly from front-fanged snakes of families Viperidae and Elapidae. On the other hand, rear-fanged snakes have been conventionally considered non-venomous, and thus their venoms have remained a largely untapped area of venomics. However, increasing documentation of life-threadening, even fatal, envenomings from rear-fanged snakes has sparked interest in their venoms. Appying bottom-up venomics we have revealed that the Duvernoy's gland secretory proteome of R. bovallii comprises a handful of toxins belonging to only three protein families, with slow-acting three-finger toxins (3FTx) that are non-toxic towards mammalian prey and show preference towards diapsid taxa representing the dominant structural and functional proteins. Our work documents for the first time 3FTxs exerting different effect in an avian model than in a reptile model. Besides, the 3FTx fractions that faithfully mimicked the irreversible iguana-immobilizing effect of the whole venom were identified through toxicovenomic analysis of R. bovallii venom on Iguana iguana. Our work underscores the importance of using biologically-relevant animal toxicity models for investigating the biological roles of venoms in an evolutionary-ecological context.