Expression and activity of cyclic and linear analogues of esculentin-1, ananti-microbial peptide from amphibian skin

Esculentin-1 is a potent anti-microbial peptide present in minute amounts i n skin secretions of Rana esculenta. It contains 46 amino-acid residues and a C-terminal disulfide bridge. We have explored the possibility of produci ng analogues of this peptide by recombinant expression in Escherichia coli of a fusion protein which is sequestered in inclusion bodies. The peptide o f interest has been inserted at the N-terminus of the protein, from which i t can be released by cyanogen bromide cleavage. The anti-microbial activiti es of the recombinant peptide as well as that of a mutant linear form devoi d of the disulfide bridge are presented. The recombinant analogues retain t he biological activity of the natural peptide, as tested with an inhibition zone assay against a variety of microorganisms. However, experiments on th e rate of bacterial killing show that gram-negative bacteria are more sensi tive to the peptides than the gram-positive bacterium, the effect of the cy clic peptide being in all cases faster than that of the linear molecule. Mo reover, the activity against gram-negative bacteria for both peptides is no t affected by salts, whereas the activity against Staphylococcus aureus is lost at high salt concentration.