Molecular and functional identification of a β‐defensin homolog in large yellow croaker (<i>Larimichthys crocea</i>)
Kexin Li, Wanru Li, Xiaojuan Chen, Xiaojuan Chen, Tian Luo, Yinnan Mu, Xinhua Chen, Xinhua Chen
Abstract
Abstract β‐defensin (BD) is a cysteine‐rich cationic antibacterial peptide that is active against a wide range of bacteria. Here, a β‐defensin homolog ( Lc BD2) was identified in large yellow croaker ( Larimichthys crocea ). The open reading frame of Lc BD2 contains 195 nucleotides, encoding a protein of 64 amino acids that possesses a typical arrangement of six conserved cysteine residues (C 31 , C 37 , C 41 , C 53 , C 59 and C 60 ). Lc BD2 transcripts were constitutively expressed in all examined tissues and significantly increased in head kidney, spleen and gills by Vibrio alginolyticus . The synthetic Lc BD2 peptide imparted antimicrobial effects on both Gram‐negative bacteria ( V . campbellii , V . parahaemolyticus , V . alginolyticus , V . harveyi and Pseudomonas plecoglossicida ) and Gram‐positive bacteria ( Bacillus subtilis ). We also observed that after treatment with synthetic Lc BD2 peptide, numerous blisters appeared on the membrane of P . plecoglossicida , which in turn may result in cell membrane breakage and bacterial death. Moreover, the synthetic Lc BD2 peptide significantly upregulated the expression levels of TNF‐α2, IL‐1β and CXCL8_L1 in monocytes/macrophages, while downregulated expression level of IL‐10. The Lc BD2 peptide also remarkedly enhanced the phagocytosis of monocytes/macrophages. These results indicate that Lc BD2 not only protects large yellow croaker against multiple bacterial pathogens but also plays a role in activation of monocytes/macrophages.