Identification and functional optimization of a novel pteroicidin-like peptide from starry flounder:...

Antimicrobial peptides of the piscidin family are key effectors of teleost innate immunity and represent promising alternatives to conventional antibiotics in aquaculture. Therefore, this study aimed to identify and characterize a novel pteroicidin-like gene (SFpte) from starry flounder (Platichthys stellatus). The deduced 64-amino-acid precursor comprised a signal peptide, 20-residue cationic α-helical mature peptide (SFpte-20; FFRHLKAIFKGARQGWRDYR), and C-terminal anionic propeptide. SFpte was constitutively expressed across tissues and significantly upregulated in the kidney and spleen following challenge with Vibrio harveyi and Streptococcus parauberis. To assess the structure-activity relationships, truncated (17-mer and 13-mer) analogs and tryptophan (Trp)-substituted variants were engineered. In silico modeling showed that truncation and Trp substitution modulated amphipathicity and membrane-transfer energetics, with H4W displaying favorable predicted membrane association (ΔG_transf = -11.1 kcal/mol). All peptides exhibited broad-spectrum antimicrobial activity (minimum inhibitory concentration 2.5-10 μM), while selected Trp variants showed enhanced antimicrobial efficiency. The scanning electron microscope confirmed bacterial membrane disruption as the primary mode of action. All analogs rapidly killed the scuticociliate Philasterides dicentrarchi. Hemolysis was concentration-dependent; specifically, the truncated 13-mer retained antimicrobial potency while inducing minimal erythrocyte lysis (<5% at 50 μM). Overall, rational truncation and strategic Trp substitution modulate efficacy and hemocompatibility, providing a basis for future in vivo evaluation of SFpte-derived analogs as marine-derived bioactive peptide templates for aquaculture applications.