Gb-piscidin: A novel antimicrobial and immunostimulant peptide from gilthead seabream (Sparus aurata) - Identification, tissue-specific expression, recombinant production, and biological evaluation.

Abstract

Fish rely on innate immunity, including antimicrobial peptides (AMPs), to combat pathogens. Piscidins are a common AMP family in fish. This study identifies and characterizes a novel piscidin (Gbpis) from gilthead seabream, highlighting its structural uniqueness, antimicrobial function, and immunomodulatory potential. The gbpis cDNA contains a 183-bp open reading frame encoding a 60-amino-acid precursor, classified as a class 1 piscidin. The mature 22-residue peptide (2314.8 Da; pI 10.11) features a disulfide bridge (Cys9-Cys16) critical for activity. Tissue-specific expression analysis revealed Gbpis mRNA in the liver, skin, head kidney, and significant upregulation in the head kidney during Aeromonas hydrophila infection. Recombinant Gbpis, expressed in E. coli with the intact disulfide bond, exhibited potent antimicrobial activity against Streptococcus iniae. Synthetic Gbpis lacking the disulfide bridge was inactive, while the bridged peptide inhibited Gram-positive bacteria, underscoring the bridge's necessity for function. In rainbow trout, Gbpis pre-treatment significantly mitigated the pro-inflammatory response to S. iniae infection. This was demonstrated by a marked reduction in the expression of il-6 and tnf-α in the head kidney. In spleen, Gbpis alone induced a potent il-6 response, which was then significantly dampened following the subsequent S. iniae challenge. These findings establish Gbpis as a novel piscidin with a structurally essential disulfide bond, demonstrating dual roles in pathogen inhibition and mitigating excessive inflammation. This study advances understanding of fish AMPs and highlights their potential in sustainable aquaculture strategies.