NRC-17

The structure-activity relations of myxinidin, a peptide derived from epidermal mucus of hagfish, Myxine glutinosa L., were investigated. Analysis of key residues allowed us to design new peptides with increased efficiency. Antimicrobial activity of native and modified peptides demonstrated the key role of uncharged residues in the sequence; the loss of these residues reduces almost entirely myxinidin antimicrobial activity, while insertion of arginine at charged and uncharged position increases antimicrobial activity compared with that of native myxinidin. Particularly, we designed a peptide capable of achieving a high inhibitory effect on bacterial growth. Experiments were conducted using both Gram-negative and Gram-positive bacteria. Nuclear magnetic resonance (NMR) studies showed that myxinidin is able to form an amphipathic α-helical structure at the N terminus and a random coil region at the C terminus.

The marine environment has been poorly explored in terms of potential new molecules possessing antibacterial activity. Antimicrobial peptides (AMPs) offer a new potential class of pharmaceuticals; however, further optimization is needed if AMPs are to find broad use as antibiotics. We focused our studies on a peptide derived from the epidermal mucus of hagfish (Myxine glutinosa L.), which was previously characterized and showed high antimicrobial activity against human and fish pathogens. In the present work, the activities of myxinidin peptide analogues were analyzed with the aim of widening the original spectrum of action of myxinidin by suitable changes in the peptide primary structure. The analysis of key residues by alanine scanning allowed for the design of novel peptides with increased activity. We identified the amino acids that are of the utmost importance for the observed antimicrobial activities against a set of pathogens comprising both Gram-negative and Gram-positive bacteria. Overall, optimized bactericidal potency was achieved by adding a tryptophan residue at the N terminus and by the simultaneous substitution of residues present in positions 3, 4, and 11 with arginine. These results indicate that the myxinidin analogues emerge as an attractive alternative for treating drug-resistant infectious diseases and provide key insights into a rational design for novel agents against these pathogens.

The mucus layer on the surface of fish consists of several antimicrobial agents that provide a first line of defense against invading pathogens. To date, little is known about the antimicrobial properties of the mucus of Arctic char (Salvelinus alpinus), brook trout (S. fontinalis), koi carp (Cyprinus carpio sub sp. koi), striped bass (Morone saxatilis), haddock (Melanogrammus aeglefinus) and hagfish (Myxine glutinosa). The epidermal mucus samples from these fish were extracted with acidic, organic and aqueous solvents to identify potential antimicrobial agents including basic peptides, secondary metabolites, aqueous and acid soluble compounds. Initial screening of the mucus extracts against a susceptible strain of Salmonella enterica C610, showed a significant variation in antimicrobial activity among the fish species examined. The acidic mucus extracts of brook trout, haddock and hagfish exhibited bactericidal activity. The organic mucus extracts of brook trout, striped bass and koi carp showed bacteriostatic activity. There was no detectable activity in the aqueous mucus extracts. Further investigations of the activity of the acidic mucus extracts of brook trout, haddock and hagfish showed that these fish species had specific activity for fish and human pathogens, demonstrating the role of fish mucus in antimicrobial protection. In comparison to brook trout and haddock, the minimum bactericidal concentrations of hagfish acidic mucus extracts were found to be approximately 1.5 to 3.0 times lower against fish pathogens and approximately 1.6 to 6.6 folds lower for human pathogens. This preliminary information suggests that the mucus from these fish species may be a source of novel antimicrobial agents for fish and human health related applications.