Discovery and characterisation of nemertides, and evaluation of their potential use for agricultural and pharmaceutical purposes

The overall aims of the projects included in this thesis were to discover, functionally characterise, explore biological safety and evaluate potential utility of cysteine-rich peptides, named alpha-nemertides, from marine worms (Nemertea sp.). One of the main outcomes of this thesis is the discovery of a new subfamily of nemertean peptide toxins, from the epidermal mucus of an unexplored marine worm ( Paper I ). Structure-activity relationships of alpha-nemertides was investigated via alanine scanning on the archetype nemertide alpha-1 ( Paper II ). Finally, a preliminary investigation of nemertide alpha-1 feeding repellence and acute toxicity was perform in vivo on pest insects ( Paper III-IV ) alongside with the analysis of its human and biological safety ( Paper III ). In Manuscript I , the discovery and initial characterisation of a new subfamily of nemertean peptide toxins from Lineus viridis is presented. The new subfamily was named delta-nemertide and the archetype, nemertide delta-1, was successfully isolated and described. Furthermore, transcriptomic analysis led to the addition of seven delta-nemertide putative sequences. Nemertide delta-1 share many similarities with the previously described nemertide alpha-1 except for a 30-fold higher potency on measured insect voltage-gated sodium channels. In Manuscript II , the study focused on determining the importance for selectivity and acute toxicity of each amino acid from nemertide alpha-1 sequence. The mutants’ toxicity was assessed in vitro on a selection of voltage-gated sodium channels and in vivo on Artemia salina . Five positions crucial for overall selectivity were highlighted and one mutant named S12A demonstrated specific selectivity to insect voltage-gated sodium channels. In Manuscript III , nemertide alpha-1 displayed feeding deterrence and feeding behaviour changes at the low molecular level on green peach aphids ( Myzus persicae ), a known pest insect. In parallel, the peptide demonstrated attractive environmental features by having very low lytic activity on liposomes and low antimicrobial effect on gram positive and negative bacteria. It also showed very low cytotoxicity on human cell lines and high temperature stability on a short period of time. In Manuscript IV , oral toxicity of nemertide alpha-1 was investigated on two mosquito’s species responsible of being diseases vectors: Anopheles coluzzii and Aedes aegypti . The peptide did not display significant feeding repellence on