A Novel Beta-Defensin Antimicrobial Peptide in Atlantic Cod with Stimulatory Effect on Phagocytic Activity

Abstract

A novel defensin antimicrobial peptide gene was identified in Atlantic cod, Gadus morhua. This three exon/two intron defensin gene codes for a peptide precursor consisting of two domains: a signal peptide of 26 amino acids and a mature peptide of 40 residues. The mature cod defensin has six conserved cysteine residues that form 1–5, 2–4 and 3–6 disulphide bridges. This pattern is typical of beta-defensins and this gene was therefore named cod beta-defensin (defb). The tertiary structure of Defb exhibits an α/β fold with one α helix and β1β2β3 sheets. RT-PCR analysis indicated that defb transcripts were present mainly in the swim bladder and peritoneum wall but could also be detected at moderate to low levels in skin, head- and excretory kidneys. In situ hybridisation revealed that defb was specifically expressed by cells located in the swim bladder submucosa and the oocytes. During embryonic development, defb gene transcripts were detectable from the golden eye stage onwards and their expression was restricted to the swim bladder and retina. Defb was differentially expressed in several tissues following antigenic challenge with Vibrio anguillarum, being up-regulated up to 25-fold in head kidney. Recombinant Defb displayed antibacterial activity, with a minimal inhibitory concentration of 0.4–0.8 µM and 25–50 µM against the Gram-(+) bacteria Planococcus citreus and Micrococcus luteus, respectively. In addition, Defb stimulated phagocytic activity of cod head kidney leucocytes in vitro. These findings imply that beta-defensins may play an important role in the innate immune response of Atlantic cod.

Molecular Characterization and In Silico Analysis of Defensin From Tor putitora (Hamilton)

“…Fish live in an environment where they are regularly exposed to pathogens [1]. Interaction of infectious agent with host in a set of environmental condition may lead to infection [2,3].…”

“…Being poikilothermic in nature, acquired immune system of fish is not well developed [4]. Antimicrobial peptides (AMPs) are widely distributed among plants, insects, vertebrates and invertebrates [1] that act as weapons of immune system [5].…”

“…In human and mouse, more than 30 while in birds 14 b-defensins have been identified [13][14][15][16]. There are few fish species including Danio rerio (zfDB1-3) [1], Tetraodon nigroviridis (tnDB 1 and 2) [1], Takifugu rubripes (fuDB) [1], Oncorhynchus mykiss (omDB [1][2][3][4] [17,18], medaka (mkDB) [19], Epinephelus coioides (ogDB) [20], Paralichthys olivaceus of (DBI 1-5) [21] where single and multiple isoforms of b-defensin have been reported.…”

“…The pattern of expression of defensins is either inducible or constitutive on the basis of tissue and stimulatory factors [1]. The destructive mechanism of bacteria involves interaction of defensin with bacterial membrane leading to insertion and permeabilization of the peptide by generating multiple pores in the bacterial membrane [25][26][27][28][29][30].…”

L-Amino Acid Oxidase, a Novel Antibacterial Protein in the Rockfish <i>Sebastes schlegeli</i>

“…Since bdefensin gene sequence was first found from the genome sequence database of zebrafish Danio rerio, green-spotted pufferfish Tetraodon nigroviridis and tiger pufferfish Takifugu rubripes (Zou et al 2007), the antibacterial activity of fish b-defensin was reported in several fishes including rainbow trout, gillhead seabream Sparus aurata, common carp Cyprinus carpio, Atlantic cod and Chinese loach Paramisgurnus dabryanus (Casadei et al 2009;Cuesta et al 2011;Marel et al 2012;Adamek et al 2013;Ruangsri et al 2013;Chen et al 2013).…”