Antimicrobial Activity of Identified Ubiquitin-40S Ribosomal Protein S27a (RPS27A), Ubiquitin-like Protein Fubi, and Ribosomal Protein (S30FAU) in the Starry Flounder (Platichthys stellatus)

Abstract

Ubiquitin-40S ribosomal protein S27a (RPS27A), ubiquitin-like protein Fubi, and ribosomal protein (S30FAU) are ubiquitin-related proteins that are involved in the regulation of immune-related functions such as cell cycle, protein expression, and apoptosis. This study aimed to confirm the molecular characteristics, gene expression analysis, and antibacterial activity of RPS27A and S30FAU identified from the starry flounder (15 starry flounders of 128.7 ± 18.2 g). An expression analysis using a normal fish showed that RPS27A was highly expressed in the head kidney, heart, and stomach. In contrast, S30FAU exhibited high expression in the stomach, heart, and head kidney. Upon simulating an artificial pathogen infection, RPS27A was highly expressed in the heart at 1 h and 3 days post-viral hemorrhagic septicemia (VHSV) infection, and had a high expression in the kidney, liver, and heart at 7 days post-Streptococcus parauberis (S. parauberis) infection. S30FAU was highly expressed in the spleen and gills at 1 day and 12 h post-VHSV infection, respectively, and exhibited a high expression in the kidney at 7 days post-S. parauberis infection. In an MIC analysis, RPS27A and S30FAU showed antimicrobial activity against all bacteria used in this study. In the biofilm assay, S30FAU was removed from S. parauberis in a concentration-dependent manner, and the cytotoxicity test showed no hemolytic activity in both RPS27A and S30FAU. Therefore, RPS27A and S30FAU of the starry flounder were confirmed to possess antimicrobial peptide abilities without limitations of cytotoxicity. This study provides valuable information on the antibacterial ability and molecular biology of the ubiquitin family isolated from the starry flounder.