Identification and characterization of a β-defensin gene involved in the immune defense response of channel catfish, Ictalurus punctatus.

Jieyao Zhu, Hong Wang, Jun Wang, Xingli Wang, Shuang Peng, Yi Geng, Kaiyu Wang, Pin Ouyang, Zhiqiong Li, Xiaoli Huang, Defang Chen

Molecular immunology 2017 May

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Antimicrobial peptides are small peptides that play important roles in a host's innate immune response. As an important antimicrobial peptide, β-defensin widely distribute in mammals, insects and plants with broad-spectrum antimicrobial activity. In this study, the β-defensin gene of the channel catfish, Ictalurus punctatus, was cloned, sequenced, and subjected to a bioinformatic analysis. The β-defensin gene of the channel catfish contains three exons and two introns, and encodes a precursor peptide consisting of two domains: a signal peptide of 24 amino acid residues and a mature peptide of 43 amino acid residues. The mature peptide is estimated to have a molecular mass of 7.1kDa and a theoretical isoelectric point of 8.21. Channel catfish β-defensin (ccBD) has six conserved cysteine residues, forming three disulfide bridges at C1-C5, C2-C4, and C3-C6, and a β-sheet in the predicted three-dimensional structure. A phylogenetic analysis suggests that ccBD belongs to the type 1 β-defensins. Real-time quantitative PCR showed that channel catfish β-defensin transcripts are constitutively expressed in various tissues in healthy fish, with highest expression in the skin. The expression of ccBD in vivo increased significantly in the head kidney (2.9-fold), gill (2.2-fold), and skin (6.6-fold) at 48h after bacterial (Edwardsiella ictaluri) challenge. In vitro, lipopolysaccharide (LPS), a bacterial mimic, induced significant changes in ccBD expression in leukocytes from the spleen (3.4-fold) and head kidney (3.9-fold) 24h after stimulation. Chemically synthesized ccBD displayed marked inhibitory activity against a broad range of bacteria. These results suggest that ccBD is involved in the innate antibacterial defenses of the channel catfish. Copyright © 2017 Elsevier Ltd. All rights reserved.

Citation

Jieyao Zhu, Hong Wang, Jun Wang, Xingli Wang, Shuang Peng, Yi Geng, Kaiyu Wang, Pin Ouyang, Zhiqiong Li, Xiaoli Huang, Defang Chen. Identification and characterization of a β-defensin gene involved in the immune defense response of channel catfish, Ictalurus punctatus. Molecular immunology. 2017 May;85:256-264