Molecular and functional identification of a β‐defensin homolog in large yellow croaker (Larimichthys crocea)

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 (LcBD2) was identified in large yellow croaker (Larimichthys crocea). The open reading frame of LcBD2 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). LcBD2 transcripts were constitutively expressed in all examined tissues and significantly increased in head kidney, spleen and gills by Vibrio alginolyticus. The synthetic LcBD2 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 LcBD2 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 LcBD2 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 LcBD2 peptide also remarkedly enhanced the phagocytosis of monocytes/macrophages. These results indicate that LcBD2 not only protects large yellow croaker against multiple bacterial pathogens but also plays a role in activation of monocytes/macrophages.

Antimicrobial Peptides: Identification of two Beta-Defensins in a Teleost Fish, the European Sea Bass (Dicentrarchus labrax)

“…Furthermore, the N-terminal portion of blunt snout bream defensin exerts an increased chemotactic activity of head kidney leukocytes, when compared to the C-terminal portion, suggesting that the N-terminal of beta-defensin might be important for this function [28]. Fish beta-defensins are also known to present antibacterial and antiviral activities [4,27,54,64]. The mechanism of action of AMPs relies on an initial interaction between the peptide and bacterial membrane [65].…”

“…Particularly for defensins, previous authors suggest that the alpha-helix might be helpful in the interaction of beta-defensin with the bacterial cell wall [66]. Indeed, synthetic and recombinant beta-defensin 2 from large yellow croaker and turbot impaired membrane morphology were recently described, leading to a severe membrane damage [27,54]. Given the similarities between these peptides and sea bass beta-defensins, particularly defensin type 1, we speculate that they may also be involved in such functions, although further studies are necessary to uncover the possible antimicrobial and chemotactic activities of each sea bass defensin.…”

“…In vitro, recombinant or synthetic defensins are able to inhibit the growth of Gram-positive and Gram-negative bacteria, as well as some viruses [24][25][26]. The immunomodulatory functions of vertebrate beta-defensins include enhanced phagocytic activity [4,27], chemotaxis of fish leukocytes [14,28] and human immature dendritic cells and T cells [29], and also modulation of immune-related genes [28].…”

Adsorption of Recombinant Human β-Defensin 2 and Two Mutants on Mesoporous Silica Nanoparticles and Its Effect against Clavibacter michiganensis subsp. michiganensis

“…Defensins are relatively short amphipathic cationic oligopeptides with variable length, sequence and structures that protect their host from a wide variety of bacteria, fungi and viruses [ 16 ]. They are usually composed of 5–100 amino acid residues, characterized by having 6–8 cysteine residues that link together to give rise to the formation of disulfide bridges [ 16 , 17 , 18 , 19 ]. According to the disposition of their disulfide bridges, defensins are subdivided into three different subfamilies: α-defensins, β-defensins and θ-defensins [ 17 ].…”

“…They are usually composed of 5–100 amino acid residues, characterized by having 6–8 cysteine residues that link together to give rise to the formation of disulfide bridges [ 16 , 17 , 18 , 19 ]. According to the disposition of their disulfide bridges, defensins are subdivided into three different subfamilies: α-defensins, β-defensins and θ-defensins [ 17 ]. Specifically, hβD2 is composed of 41 amino acid residues and as the other β-defensins bears a 6-cysteine motif to be stabilized by three conserved disulfide bridges; hβD2 antimicrobial activity has been evaluated against different human pathogenic strains such as Actinobacillus actinomycetemcomitans , Candida albicans and Pseudomona aeruginosa [ 19 , 20 ].…”