Molecular cloning and characterization of the two putative toxins expressed in the venom of the devil stinger Inimicus japonicus.

Various proteins are involved in fish venom toxicity, but limited information is available regarding their structure and mode of action. Here, we analyzed RNA transcripts in the dorsal spine of the devil stinger Inimicus japonicus using next-generation sequencing (NGS), and identified two putative protein toxins, a natterin-like protein (Ij-natterin) and a phospholipase A (Ij-PLA), as well as a previously reported stonustoxin-like protein. The deduced amino acid sequence of Ij-natterin suggested that it acts as a pore-forming toxin through the cooperation of the N-terminal lectin-like domain and the C-terminal pore-forming domain. Ij-PLA showed significant homology with secreted Ca-dependent PLAs from snake venom and mammals (sPLA-I/II). The recombinant Ij-PLA protein exhibited PLA activity in the absence of Ca, in contrast to canonical sPLA-I/II. Comparison of the amino acid sequences of Ij-PLA with the other sPLA-I/II suggests that the C-terminal extended peptide region of Ij-PLA is involved in its Ca-independent activity.