Venom-gland Transcriptomic, Venomic, and Antivenomic Profiles of the Spine-bellied Sea Snake (Hydrophis curtus) from the South China Sea

Abstract

Background: A comprehensive evaluation of the -omic profiles of venom is important for understanding the potential function and evolution of snake venom. Here, we conducted an integrated multi-omics-analysis to unveil the venom-transcriptomic and venomic profiles in a same group of spine-bellied sea snakes (Hydrophis curtus) from the South China Sea, where the snake is a widespread species and might generate regionally-specific venom potentially harmful to human activities. The capacity of two heterologous antivenoms to immunocapture the H. curtus venom was determined for an in-depth evaluation of their rationality in treatment of H. curtus envenomation. In addition, a phylogenetic analysis by maximum likelihood was used to detect the adaptive molecular evolution of full-length toxin-coding unigenes.Results: A total of 90,909,384 pairs of clean reads were generated via Illumina sequencing from a pooled cDNA library of six specimens, and yielding 148,121 unigenes through de novo assembly. Sequence similarity searching harvested 63,845 valid annotations, including 63,789 non-toxin-coding and 56 toxin-coding unigenes belonging to 22 protein families. Three protein families, three-finger toxins (3-FTx), phospholipase A2 (PLA2), and cysteine-rich secretory protein, were detected in the venom proteome. 3-FTx (27.15% in the transcriptome/41.94% in the proteome) and PLA2 (59.71%/49.36%) were identified as the most abundant families in the venom-gland transcriptome and venom proteome. In addition, 24 unigenes from 11 protein families were shown to have experienced positive selection in their evolutionary history, whereas four were relatively conserved throughout evolution. Commercial Naja atra antivenom exhibited a stronger capacity than Bungarus multicinctus antivenom to immunocapture H. curtus venom components, especially short neurotoxins, with the capacity of both antivenoms to immunocapture short neurotoxins being weaker than that for PLA2s.Conclusions: Our study clarified the venom-gland transcriptomic and venomic profiles along with the within-group divergence of a H. curtus population from the South China Sea. Adaptive evolution of most venom components driven by natural selection appeared to occur rapidly during evolutionary history. Notably, the utility of commercial N. atra and B. multicinctus antivenoms against H. curtus toxins was not comprehensive; thus, the development of species-specific antivenom is urgently needed.

Venom of the Annulated Sea Snake Hydrophis cyanocinctus: A Biochemically Simple but Genetically Complex Weapon

“…Specifically, the expression of acidic and basic PLA 2 s was approximately 1.9- and 1.8-fold higher in the Xisha population than in the Haikou population, respectively. Furthermore, the ratio of SNX to LNX (1:2) in the Xisha population was opposite to that in the Hara (1.8:1) and Haikou (2.5:1) populations, and such an inconsistent divergence has also been found in H. curtus venoms [ 20 , 22 , 24 ]. This suggests that the potential symptoms of snakebites caused by H. cyanocinctus might vary among populations.…”

“…Of the studies carried out in the past decade to assess the diversity of toxin-coding genes at the venom-gland transcriptomic level in snakes, only four focused on sea snakes ( Acalyptophis peronii , H. curtus and Hydrophis platurus ) [ 27 , 28 , 29 , 35 ]. Compared with H. curtus (22 protein families, Figure 3 B,C; [ 24 , 29 ]) and H. platurus (15 protein families, Figure 3 D; [ 27 ]), H. cyanocinctus (24 protein families) displayed a relatively high diversity of toxin-coding unigenes from the venom-gland transcriptome. Similar to the venom-gland transcriptome reported previously for sea snakes [ 26 , 27 , 28 , 34 ], the PLA 2 and 3-FTx families constituted the most abundant components in the toxin-coding unigenes of the H. cyanocinctus venom-gland transcriptome.…”

“…Briefly, 17 of 27 toxin-coding unigenes from H. cyanocinctus were found to exhibit positive selection according to the likelihood ratio between M1 and M2, and this was verified by that between M7 and M8 (the results are not shown as they are nearly identical to those for M1 and M2). The percentage (63%, 17/27) of toxin-coding unigenes that underwent positive selection in H. cyanocictus was significantly lower than that for Crotalus adamanteus (89%, 24/27; [ 50 ]) and H. curtus (73%, 24/33; [ 24 ]), and it would even be much lower if the sequences analysed by yn00 were taken into account. Notably, all of the unigenes from the 3-FTx, PLA 2 and CRISP families in H. cyanocictus , which could be detected in high abundance at the protein level and might have a practical function in predation and defence, were found to undergo positive selection.…”

“… Comparison of the overall venom-gland transcriptomic profiles of three sea snakes: ( A ) current study; ( B – D ) cited and rearranged from Zhao et al [ 24 ], Tan et al [ 29 ] and Durban et al [ 27 ], respectively. NC, non-conventional neurotoxin; SVSP, snake venom serine proteinase; AchE, acetylcholinesterase.…”

“…Compared with their terrestrial relatives, sea snakes tend to simplify venom components to the extreme at the protein level [ 18 ]. Sea-snake venoms are mainly comprised of three-finger toxins (3-FTxs) and phospholipase A 2 (PLA 2 ) [ 19 , 20 , 21 , 22 , 23 , 24 ], with the short- and long-chain neurotoxins of 3-FTxs being the major and strong neurotoxic components [ 25 , 26 ]. Most sea snakes have to deal with fast-moving prey and, as such, the lethal neurotoxic venom can help them to quickly paralyze or kill prey almost instantaneously without letting them escape and avoid hurting themselves in the prey struggle [ 18 ].…”