Discovery of 194 Unreported Conopeptides and Identification of a New Protein Disulfide Isomerase in Conus caracteristicus Using Integrated Transcriptomic and Proteomic Analysis

Han Zhang,Baoting Nong,Xinghua Pan,Lei Wang,Yinbin Qiu,Fahui Gong

doi:10.3389/fmars.2022.792908

Abstract

Current ConoServer database accumulates 8,134 conopeptides from 122 species of cone snail, which are pharmaceutically attractive marine resource. However, many more conopeptides remain to be discovered, and the enzymes involved in their synthesis and processing are unclear. In this report, firstly we screened and analyzed the differentially expressed genes (DEGs) between venom duct (VD) and venom bulb (VB) of C. caracteristicus, and obtained 3,289 transcripts using a comprehensive assembly strategy. Then using de novo deep transcriptome sequencing and analysis under a strict merit, we discovered 194 previously unreported conopeptide precursors in Conus caracteristicus. Meanwhile, 2 predicted conopeptides from Consort were verified using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Furthermore, we demonstrated that both VD and VB of C. caracteristicus secreted hundreds of different conotoxins, which showed a high diversity among individuals of the species. Finally, we identified a protein disulfide isomerase (PDI) gene, which, functioning for intramolecular disulfide-bond folding, was shared among C. caracteristicus, C. textile, and C. bartschi and was the first PDI identified with five thioredoxin domains. Our results provide novel insights and fuel further studies of the molecular evolution and function of the novel conotoxins.

Highlights

Cone snails, which are carnivorous marine gastropod mollusks, produce a cocktail of venom peptides, known as conotoxins or conopeptides, that are used in predation, defense, or competition (Gao et al, 2017)
We present conopeptide diversity among individuals and verify these superfamilies using liquid chromatography-mass spectrometry/mass spectrometry (LCMS/MS)
We have accidentally identified a new protein disulfide isomerase (PDI) gene, which is highly homologous to sequences in C. textile and C. bartschi

Summary

Introduction

Cone snails, which are carnivorous marine gastropod mollusks, produce a cocktail of venom peptides, known as conotoxins or conopeptides, that are used in predation, defense, or competition (Gao et al, 2017). Based on sequence similarities with signal peptides in the ConoServer database, conopeptides are currently classified into 27 gene superfamilies (A, B1, B2, B3, C, D, E, F, G, H, I1, I2, I3, J, K, L, M, N, O1, O2, O3, P, Q, S, T, V, and Y) (Kaas et al, 2008, 2010, 2012; Puillandre et al, 2012; Ye et al, 2012; Aguilar et al, 2013; Dutertre et al, 2013; Luo et al, 2013; Lu et al, 2014; Peng et al, 2016; Fu et al, 2018; Yao et al, 2019; Li et al, 2020) and 13 additional putative gene superfamilies (Espiritu et al, 2001; Biggs et al, 2010; Kaas et al, 2010, 2012). Due to the high selectivity for various ion channels and nerve receptors, conotoxins have become an important tool in neuroscience research and have a great potential for use in the development of novel drugs (Wermeling, 2005; Han et al, 2008; Lebbe et al, 2014; Pan, 2019; Shen, 2019)

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