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Structure-microbicidal activity relationship of synthetic fragments derived from the antibacterial alpha-helix of human lactoferrin.

Journal article
Authors Liliana Håversen
Nahid Kondori
L Baltzer
Lars Åke Hanson
G T Dolphin
K Dunér
Inger Mattsby-Baltzer
Published in Antimicrobial agents and chemotherapy
Volume 54
Issue 1
Pages 418-25
ISSN 1098-6596
Publication year 2010
Published at Wallenberg Laboratory
Institute of Biomedicine, Department of Microbiology and Immunology
Institute of Biomedicine, Department of Infectious Medicine
Pages 418-25
Language en
Keywords Amino Acid Sequence, Amino Acids, chemistry, Anti-Bacterial Agents, chemical synthesis, chemistry, pharmacology, Candida albicans, drug effects, Escherichia coli, drug effects, Humans, Hydrogen-Ion Concentration, Kinetics, Lactoferrin, chemical synthesis, chemistry, pharmacology, Limulus Test, Lipopolysaccharides, pharmacology, Metals, chemistry, Microbial Sensitivity Tests, Milk, Human, microbiology, Molecular Mimicry, Molecular Sequence Data, Peptide Fragments, chemical synthesis, chemistry, pharmacology, Protein Conformation, Sodium Chloride, chemistry, Staphylococcus aureus, drug effects, Structure-Activity Relationship
Subject categories Medical microbiology, Pharmaceutical microbiology


There is a need for new microbicidal agents with therapeutic potential due to antibiotic resistance in bacteria and fungi. In this study, the structure-microbicidal activity relationship of amino acid residues 14 to 31 (sequence 14-31) from the N-terminal end, corresponding to the antibacterial alpha-helix of human lactoferrin (LF), was investigated by downsizing, alanine scanning, and substitution of amino acids. Microbicidal analysis (99% killing) was performed by a microplate assay using Escherichia coli, Staphylococcus aureus, and Candida albicans as test organisms. Starting from the N-terminal end, downsizing of peptide sequence 14-31 showed that the peptide sequence 19-31 (KCFQWQRNMRKVR, HL9) was the optimal length for antimicrobial activity. Furthermore, HL9 bound to lipid A/lipopolysaccharide, as shown by neutralizing endotoxic activity in a Limulus assay. Alanine scanning of peptide sequence 20-31 showed that Cys20, Trp23, Arg28, Lys29, or Arg31 was important for expressing full killing activity, particularly against C. albicans. Substituting the neutral hydrophilic amino acids Gln24 and Asn26 for Lys and Ala (HLopt2), respectively, enhanced microbicidal activity significantly against all test organisms compared to the amino acids natural counterpart, also, in comparison with HL9, HLopt2 had more than 10-fold-stronger fungicidal activity. Furthermore, HLopt2 was less affected by metallic salts than HL9. The microbicidal activity of HLopt2 was slightly reduced only at pH 7.0, as tested in the pH range of 4.5 to 7.5. The results showed that the microbicidal activity of synthetic peptide sequences, based on the antimicrobial alpha-helix region of LF, can be significantly enhanced by optimizing the length and substitution of neutral amino acids at specific positions, thus suggesting a sequence lead with therapeutic potential.

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