Abstract
Lactoferrin (LF) is a multifunctional protein with a broad spectrum of antimicrobial activities. In this study, we investigated the antimicrobial activity of LF against the potato common scab pathogen Streptomyces scabiei, which causes severe damage to potato tubers. LF derived from bovine (bLF) had much higher activity against S. scabiei than human LF. The minimal inhibitory concentration of bLF was 3.9 μM. The effects of both apo-bLF (iron-free) and holo-bLF (iron-saturated) on S. scabiei were not different. Bovine lactoferricin (LFcinB), a short peptide with a length of 25 amino acid residues located in the N-terminal region of bLF, showed antimicrobial activity against S. scabiei, similar to that of bLF. These results indicated that the antimicrobial activity of bLF against S. scabiei cannot be attributed to its iron-chelating effect but to the bioactivity of its peptides. When S. scabiei was treated with the fusion protein of mCherry-LFcinB (red fluorescent protein) expressed in Escherichia coli, the pseudohyphal cells instantly glowed, indicating that the peptide electrostatically binds to the surface of S. scabiei. An assay of synthetic peptides, with modified number of arginine (Arg) and tryptophan (Trp) residues based on the antimicrobial center (RRWQWR) of LFcinB showed that Trp residues are implicated in the antimicrobial activity against S. scabiei; however, Arg residues are also necessary to carry Trp residues to the cell surface to fully exert its activity. Although the single amino acid effect of Trp had low activity, Trp derivatives showed much higher activity against S. scabiei, suggesting that the derivatives effectively bind to the cell surface (cell membrane) by themselves without a carrier. Thus, amino acid derivatives might be considered effective and alternative antimicrobial substances.
Highlights
Lactoferrin (LF), a member of the transferrin family, is a multifunctional glycoprotein present in milk, sudor, lacrima, saliva, and blood
The results showed that both Human-derived LF (hLF) and bovine-derived LF (bLF) had antimicrobial activity against S. scabiei and bLF was more potent than hLF (Fig 1)
To understand whether the iron-chelating effect is involved in the antimicrobial action of bLF, we used apo-bLF and holo-bLF; both apo- and holo-bLFs showed the same profiles in their antimicrobial activities (Fig 2), indicating that iron-chelating effect is not involved in its antimicrobial action
Summary
Lactoferrin (LF), a member of the transferrin family, is a multifunctional glycoprotein present in milk, sudor, lacrima, saliva, and blood. LF has various properties, including antioxidant, anticancer, and wound healing [1,2,3] It performs a wide range of antimicrobial activities, thereby, playing a critical role in protecting newborn infants from infection [4]. Antimicrobial effect and mechanism of lactoferrin against Streptomyces scabiei including viruses, bacteria, and fungi [5,6,7,8,9,10]. In this study, we investigated the effect of LF on the potato common scab pathogen Streptomyces scabiei, an actinomycete, which causes an economically important disease in potato tubers worldwide and is difficult to control in the field [18, 19]
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