Bass Hepcidin Synthesis, Solution Structure, Antimicrobial Activities and Synergism, and in Vivo Hepatic Response to Bacterial Infections

Abstract

Bass hepcidin was purified from the gill of hybrid striped bass (Morone chrysops ؋ Morone saxatilis) based on antimicrobial activity against Escherichia coli. This 21-amino acid peptide has 8 cysteines engaged in 4 disulfide bonds and is very similar to human hepcidin, an antimicrobial peptide with iron regulatory properties. To gain insight into potential role(s) of bass hepcidin in innate immunity in fish, we synthesized the peptide, characterized its antimicrobial activities in vitro, determined its solution structure by NMR, and quantified hepatic gene expression in vivo following infection of bass with the fish pathogens, Streptococcus iniae or Aeromonas salmonicida. Its structure is very similar to that of human hepcidin, including the presence of an antiparallel ␤-sheet, a conserved disulfide-bonding pattern, and a rare vicinal disulfide bond. Synthetic bass hepcidin was active in vitro against Gram-negative pathogens and fungi but showed no activity against key Gram-positive pathogens and a single yeast strain tested. Hepcidin was non-hemolytic at microbicidal concentrations and had lower specific activity than moronecidin, a broad spectrum, amphipathic, ␣-helical, antimicrobial peptide constitutively expressed in bass gill tissue. Good synergism between the bacterial killing activities of hepcidin and moronecidin was observed in vitro. Hepcidin gene expression in bass liver increased significantly within hours of infection with Gram-positive (S. iniae) or Gram-negative (A. salmonicida) pathogens and was 4 -5 orders of magnitude above base-line 24 -48 h post-infection. Our results suggest that hepcidin plays a key role in the antimicrobial defenses of bass and that its functions are potentially conserved between fish and human.

Multiple Hepcidins in a Teleost Fish, Dicentrarchus labrax: Different Hepcidins for Different Roles

“…It is highly likely that other Hamp2 mature peptides may present differential antimicrobial activity. Similar Hamp2 antimicrobial activities have been reported for P. olivaceus (17), M. chrysops 3 M. saxatilis (72), Oreochromis mossambicus (18), Cynoglossus semilaevis (65), Epinephelus coioides (24), Pseudosciaena crocea (22), and Acanthopagrus schlegelii (23), with varying spectrums of activity.…”

A Novel Isoform of the Hepatic Antimicrobial Peptide, Hepcidin (Hepc-CB1), from a Deep-Sea Fish, the Spinyjaw Greeneye Chlorophthalmus bicornis (Norman, 1939): Molecular Characterisation and Phylogeny

“…Highly conserved cysteine residues in the mature peptide regions form the core domain signature, which serves as the disulphide-bridged back bone of the b-hairpin-like structures. The structural organisation and bonding pattern of Hepc-CB1 are similar to the earlier reported hepcidins of A. schlegelli [14], humans [36] and bass [37]. The predicted cleavage site of signal peptide between Ala 24 and Gly 25 of C. bicornis Hepc-CB1 is exactly similar to that of the cleavage sites of A. schlegelli hepc-2 and hepc-6 (Fig.…”

Lipopolysaccharide, a Key Molecule Involved in the Synergism between Temporins in Inhibiting Bacterial Growth and in Endotoxin Neutralization

“…These include the combination of magainin 2 and PGLa from Xenopus laevis (57), between different isoforms of dermaseptins (58), cathelicidins, and defensins (59), and between hepcidin and moronecidin, isolated from bass gill tissue (60). However, except for magainin-2 and PGLa, which were found to form heterodimers in solution, and partially for temporins (as explained below), the molecular mechanism accounting for these findings is not yet known.…”