Venom duct origins of prey capture and defensive conotoxins in piscivorous Conus striatus

Abstract

The venom duct origins of predatory and defensive venoms has not been studied for hook-and-line fish hunting cone snails despite the pharmacological importance of their venoms. To better understand the biochemistry and evolution of injected predatory and defensive venoms, we compared distal, central and proximal venom duct sections across three specimens of C. striatus (Pionoconus) using proteomic and transcriptomic approaches. A total of 370 conotoxin precursors were identified from the whole venom duct transcriptome. Milked defensive venom was enriched with a potent cocktail of proximally expressed inhibitory α-, ω- and μ-conotoxins compared to milked predatory venom. In contrast, excitatory κA-conotoxins dominated both the predatory and defensive venoms despite their distal expression, suggesting this class of conotoxin can be selectively expressed from the same duct segment in response to either a predatory or defensive stimuli. Given the high abundance of κA-conotoxins in the Pionoconus clade, we hypothesise that the κA-conotoxins have evolved through adaptive evolution following their repurposing from ancestral inhibitory A superfamily conotoxins to facilitate the dietary shift to fish hunting and species radiation in this clade.

Comparative Venomics of C. flavidus and C. frigidus and Closely Related Vermivorous Cone Snails

“…C. flavidus expressed 206 conotoxin precursor sequences classified into 21 gene superfamilies, while C. frigidus expressed 107 conotoxin precursor sequences from 17 gene superfamilies ( Figure 1 , Table 1 and Table S1 ). This level of similarity is reminiscent of the overlap observed within the venoms of individuals from the same species [ 20 , 21 , 22 , 23 ], confirming C. flavidus and C. frigidus are indeed closely related. Surprisingly, the conotoxin sequence number was ≈2 fold higher, and the total read number ≈9.5 fold higher in the C. flavidus venom duct transcriptome compared to that of C. frigidus , although similarities in the relative distribution of these transcripts across the superfamilies was maintained ( Figure 1 B, Table 1 ).…”

“…Interestingly, the expression of species specific conotoxins was higher in C. flavidus and C. tribblei compared to C. frigidus and C. lenavati, suggesting that evolutionary pressures favoured less sequence retention and/or diversification in these latter species, perhaps due to different species-specific selection pressures. In contrast, three closely related fish hunting species ( C. catus, C. striolatus , and C. striatus ) of the Pionoconus clade showed <2% sequence identity despite having a similar superfamily profile [ 21 , 40 , 41 ]. On the basis of these findings, we suggest that diversifying selection pressures might be higher for more recently evolved fish-hunting (and likely mollusc-hunting) species compared to worm-hunting species of cone snails, reflecting adaptive divergence around new targets for capture prey and defence.…”

“…The I superfamily is relatively common across worm-hunting cone snail species ( Table S4 ) [ 18 , 27 , 30 , 31 , 32 , 33 , 34 ], but less abundant in fish hunting cone snails [ 20 , 21 , 22 , 41 , 44 ], suggesting these conotoxins may have evolved for predation on worms. I superfamily sequences showed a high level of high diversity between C. flavidus and C. frigidus transcriptomes, suggesting species-specific specialisation.…”

“…Contryphans are another major class of conotoxins widely distributed across fish- [ 21 , 36 , 40 ], mollusc- [ 45 , 46 ], and worm-hunting [ 46 , 47 ] lineages. Although the biological significance and pharmacological properties of contryphans remain to be defined, their abundance at both the transcriptomic and proteomic levels suggests they play a major role C. flavidus and C. frigidus .…”

Coordinated adaptations define the ontogenetic shift from worm- to fish-hunting in a venomous cone snail

“…As seen in sister species 37,38,39 , the A-superfamily was structurally and functionally diverse in adult C. magus, including vertebrate-active κA-conotoxins (IV cysteine framework, CC-C-C-C-C) dominating the proximal VG (47.6% vs 25.5% in distal) and α-conotoxins (I cysteine framework, CC-C-C) preferentially expressed in the distal VG (6.4% vs 0.8% in proximal). We identi ed two new putative κA-conotoxins that contained conserved threonines at positions 7, 9 and 10 that are often post-translationally glycosylated 40 .…”