Potassium Efflux Induced by a New Lactoferrin-Derived Peptide Mimicking the Effect of Native Human Lactoferrin on the Bacterial Cytoplasmic Membrane

M. Viejo-Díaz^1,2¶, M. T. Andrés^2¶, J. Pérez-Gil³, M. Sánchez⁴, and J. F. Fierro^1,2*

¹Department of Functional Biology (Microbiology), Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain; fax: +34-985-103533; E-mail: jffierro@correo.uniovi.es

²Laboratory of Oral Microbiology, School of Stomatology, University of Oviedo, 33006 Oviedo, Spain

³Department of Biochemistry and Molecular Biology I, Faculty of Biology, Complutense University, 28040 Madrid, Spain

⁴Department of Medicine (Pharmacology), Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain

^* To whom correspondence should be addressed.

^¶ Contributed equally to this report.

Received April 27, 2002; Revision received May 21, 2002

---

A 31-amino acid synthetic peptide (NH₂-FFSASCVPGADKGQFPNLCRLCAGTGENKCA-COOH) was chemically synthesized based on the amino acid sequence of a region of human lactoferrin homologous to other sequences present in the N- and C-lobes of all members of the transferrin family proteins. The peptide, termed kaliocin-1, and lactoferrin showed a bactericidal effect in assays performed in low-ionic-strength conditions. This is the first time that it is shown that the antimicrobial effect of lactoferrin depends on the extracellular cation concentration. The antimicrobial effect of kaliocin-1 was lower than that of human lactoferrin, but their activities were inhibited by Na⁺ or K⁺ in a cation concentration-dependent manner. In addition, the peptide was able to mimic native lactoferrin, inducing K⁺-efflux and a selective dissipation of the transmembrane electrical potential of Escherichia coli cells without causing extensive damage to the outer and inner bacterial membranes. In contrast, the peptide, but not lactoferrin, was able to permeabilize different ions through liposomal membranes. The hypothetical interaction of kaliocin-1 with a bacterial membrane compound is discussed based in the different ion flux induced on cellular and artificial membranes as well as data from circular dichroism assays. Kaliocin-1 was not cytotoxic and could be a suitable model for the design of analogs able to mimic the antibacterial effect of human lactoferrin.

---

KEY WORDS: antimicrobial peptide, lactoferrin-derived peptide, lactoferrin, transferrin, lactoferricin, kaliocin, electrical potential, membrane permeabilization

---