Kaliocin-1

The synthetic peptides Lfpep and kaliocin-1 include the sequences from positions 18 to 40 and 153 to 183 of human lactoferrin, respectively. Lfpep is a cationic peptide with bactericidal and giardicidal effects, whereas kaliocin-1 is a novel bactericidal peptide that corresponds to a highly homologous sequence present in the transferrin family of proteins. Both peptides presented fungicidal activity against Candida spp., including fluconazole- and amphotericin B-resistant clinical isolates. Lfpep exhibited higher antifungal activity (8- to 30-fold) and salt resistance than kaliocin-1. The killing activity of Lfpep was mediated by its permeabilizing activity on Candida albicans cells, whereas kaliocin-1 was unable to disrupt the cytoplasmic membrane, as indicated by its inability to allow permeation of propidium iodide and the small amount of K+ released. The amino acid sequence of kaliocin-1 includes the "multidimensional antimicrobial signature" conserved in disulfide-containing antimicrobial peptides and a striking similarity to brevinin-1Sa, an antimicrobial peptide from frog skin secretions, exhibiting a "Rana box"-like sequence. These features may be of interest in the design of new antifungals.

Kaliocin-1 is a 31-residue peptide derived from human lactoferrin, and with antimicrobial properties that recapitulate those of its 611 amino acid parent holoprotein. As kaliocin-1 is a cysteine-stabilized peptide, it was of interest to determine whether it contained a multidimensional gamma-core signature recently identified as common to virtually all classes of disulfide-stabilized antimicrobial peptides. Importantly, sequence and structural analyses identified an iteration of this multidimensional antimicrobial signature in kaliocin-1. Further, the gamma-core motif was found to be highly conserved in the transferrin family of proteins across the phylogenetic spectrum. Previous studies suggested that the mechanism by which kaliocin-1 exerts anti-candidal efficacy depends on mitochondrial perturbation without cell membrane permeabilization. Interestingly, results of a yeast two-hybrid screening analysis identified an interaction between kaliocin-1 and mitochondrial initiation factor 2 in a Saccharomyces cerevisiae model system. Taken together, these data extend the repertoire of antimicrobial peptides that contain gamma-core motifs, and suggest that the motif is conserved within large native as well as antimicrobial peptide subcomponents of transferrin family proteins. Finally, these results substantiate the hypothesis that antimicrobial activity associated with host defense effector proteins containing a gamma-core motif may correspond to targets common to fungal mitochondria or their bacterial ancestors.

The aim of this study was to explore the antibacterial peptides derived from dromedary lactoferrin (LFc). The LFc was purified from colostrum using a batch procedure with a cation exchange chromatography support and was hydrolyzed with pepsin to generate peptic digest. This peptic digest was fractionated by cation exchange chromatography, and the antilisterial activity of LFc, peptic digest, and obtained fractions was investigated using the bioscreen method. The growth of Listeria innocua ATCC 33090 and LRGIA 01 strains was not inhibited by LFc and its hydrolysates. Two fractions of dromedary lactoferrin peptic hydrolysate were active against both strains. A tandem mass spectroscopy analysis revealed that the 2 active fractions comprised at least 227 different peptides. Among these peptides, 9 found in the first fraction had at least 50% similarity with 10 known antimicrobial peptides (following sequence alignments with the antimicrobial peptide database from the University of Nebraska Medical Center, Omaha). Whereas 9 of these peptides presented homology with honeybee, frog, or amphibian peptides, the 10th peptide, F152SASCVPCVDGKEYPNLCQLCAGTGENKCACSSQEPYFGY192 (specifically found in 1 separated fraction), exibited 54% homology with a synthetic antibacterial peptide (AP00481) derived from human lactoferrin named kaliocin-1. Similarly, the second fraction contained 1 peptide similar to lactoferrampin B, an antibacterial peptide derived from bovine milk. This result suggests that peptic hydrolysis of LFc releases more active antimicrobial peptides than their protein source and thus provides an opportunity for their potential use to improve food safety by inhibiting undesirable and spoilage bacteria.