Turbot (Scophthalmus maximus) Nk-lysin induces protection against the pathogenic parasite Philasterides dicentrarchi via membrane disruption

10 pages, 6 figuresP. dicentrarchi is one of the most threatening pathogens for turbot aquaculture. This protozoan ciliate is a causative agent of scuticociliatosis, which is a disease with important economic consequences for the sector. Neither vaccines nor therapeutic treatments are commercially available to combat this infection. Numerous antimicrobial peptides (AMPs) have demonstrated broad-spectrum activity against bacteria, viruses, fungi, parasites and even tumor cells; an example is Nk-lysin (Nkl), which is an AMP belonging to the saposin-like protein (SAPLIP) family with an ability to interact with biological membranes. Following the recent characterization of turbot Nkl, an expression plasmid encoding Nkl was constructed and an anti-Nkl polyclonal antibody was successfully tested. Using these tools, we demonstrated that although infection did not clearly affect nkl mRNA expression, it induced changes at the protein level. Turbot Nkl had the ability to inhibit proliferation of the P. dicentrarchi parasite both in vivo and in vitro. Moreover, a shortened peptide containing the active core of turbot Nkl (Nkl71-100) was synthesized and showed high antiparasitic activity with a direct effect on parasite viability that probably occurred via membrane disruption. Therefore, the nkl gene may be a good candidate for genetic breeding selection of fish, and either the encoded peptide or its shortened analog is a promising antiparasitic treatment in aquacultureThis work was funded by the projects AGL2014-51773-C3 and BIO2017-82851-C3-1-R from the Spanish Ministerio de Economía y Competitividad, Proyecto Intramural Especial, PIE 201230E057 from Agencia Estatal Consejo Superior de Investigaciones Científicas (CSIC), IN607B 2016/12 from Consellería de Economía, Emprego e Industria (GAIN), Xunta de Galicia, and by the ParaFishControl project, which received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No. 634429. Raquel Lama thanks GAIN, Xunta de Galicia, for her predoctoral contract (IN606A-2017/011)Peer reviewe