Gunnar Dolphin

Human Lactoferrin and Peptides Derived from a Surface-Exposed Helical Region Reduce Experimental Escherichia coli Urinary Tract Infection in Mice

ABSTRACT Lactoferrin (LF) is a multifunctional immunoregulatory protein that has been associated with host defense at mucosal surfaces through its antibacterial properties. The antibacterial and anti-inflammatory properties of LF were further explored with an animal model of experimental urinary tract infection. Bovine LF (bLF), human LF (hLF), and synthetic peptide sequences based on the antibacterial region of hLF (amino acid residues 16 to 40 [HLD1] and 18 to 40 [HLD2]) were given orally to female mice 30 min after the instillation of 108Escherichia coli bacteria into the urinary bladder. The control groups received phosphate-buffered saline or water. C3H/Tif mice were treated with hLF or bLF, and C3H/HeN mice were treated with bLF only. The numbers of bacteria in the kidneys and bladder of C3H/Tif and C3H/HeN mice were significantly reduced 24 h later by the LF treatments compared to the findings for the control group. The hLF-treated group showed the strongest reduction compared with the vehicle-treated-group (P values were 0.009 and 0.0001 for the kidneys and bladder, respectively). The urinary leukocyte response was diminished in the hLF-treated group. The hLF treatment also significantly reduced the urinary interleukin-6 (IL-6) levels at 2 h and the systemic IL-6 levels at 24 h after infection (P values were 0.04 and < 0.002, respectively). In the bLF-treated animals, no such strong anti-inflammatory effects were obtained. In another series of experiments, C3H/Tif mice perorally treated with HLD1 or HLD2 also showed reduced numbers of bacteria in the kidneys compared with the vehicle-treated mice, although the results were significantly different only for HLD2 (P < 0.01). Analysis of urine from hLF-fed C3H/Tif mice showed that hLF was excreted into the urinary tract at 2 h after feeding. Testing of the in vitro bactericidal activity of LF (1 mg/ml) or the peptides (0.1 mg/ml) in mouse urine against the E. coli bacteria revealed moderate killing only by HLD2. In conclusion, these results demonstrate for the first time that oral administration of hLF or peptides thereof is effective in reducing infection and inflammation at a remote site, the urinary tract, possibly through transfer of hLF or its peptides to the site of infection via renal secretion. The antibacterial mechanism is suggested to involve bactericidal capacities of LF, fragments thereof, or its peptides.

Structure-Microbicidal Activity Relationship of Synthetic Fragments Derived from the Antibacterial α-Helix of Human Lactoferrin

ABSTRACT 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 α-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 α-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.

Fungicidal activity of human lactoferrin-derived peptides based on the antimicrobial αβ region

Owing to the increasing number of infections in hospitalised patients caused by resistant strains of fungi, there is a need to develop new therapeutic agents for these infections. Naturally occurring antimicrobial peptides may constitute models for developing such agents. A modified peptide sequence (CFQWKRAMRKVR; HLopt2) based on amino acid residues 20-31 of the N-terminal end of human lactoferrin (hLF) as well as a double-sized human lactoferricin-like peptide (amino acid residues 16-40; HLBD1) were investigated for their antifungal activities in vitro and in vivo. By in vitro assay, HLopt2 was fungicidal at concentrations of 12.5-25 μg/mL against Cryptococcus neoformans, Candida albicans, Candida krusei, Candida kefyr and Candida parapsilosis, but not against Candida glabrata. HLopt2 was demonstrated to have ≥ 16-fold greater killing activity than HLBD1. By inducing some helical formation caused by lactam bridges or by extending the assay time (from 2h to 20 h), HLBD1 became almost comparable with HLopt2 in its fungicidal activity. Killing of C. albicans yeast cells by HLopt2 was rapid and was accompanied by cytoplasmic and mitochondrial membrane permeabilisation as well as formation of deep pits on the yeast cell surface. In a murine C. albicans skin infection model, atopic treatment with the peptides resulted in significantly reduced yields of Candida from the infected skin areas. The antifungal activities of HLopt2 in vitro and in vivo suggest possible potential as a therapeutic agent against most Candida spp. and C. neoformans. The greatly improved antifungal effect of the lactam-modified HLBD1 indicates the importance of amphipathic helix formation for lethal activity.

Multifunctional Folded Polypeptides from Peptide Synthesis and Site‐Selective Self‐Functionalization—Practical Scaffolds in Aqueous Solution

The site selectivity of His‐mediated lysine and ornithine side‐chain acylation in a designed four‐helix bundle protein scaffold was mapped by reaction of several polypeptides with one equivalent of mono‐p‐nitrophenyl fumarate in aqueous solution at pH 5.9 and room temperature followed by an analysis of the degrees and sites of acylation. Integration of the HPLC chromatograms of the acylated polypeptides and trypsin cleavage followed by mass spectrometry analysis of the tryptic fragments provided the experimental evidence. Based on these and previously published results a strategy was developed for the site‐selective and stepwise incorporation of three residues into a folded polypeptide in aqueous solution at room temperature. The first substituent was incorporated by reaction of a 1.7‐fold excess of the corresponding active ester with the polypeptide at pH 5.9, the second substituent was introduced in a 3‐fold excess after the pH value was raised to 8, and the third substituent was incorporated by reaction of a 10‐fold excess with the polypeptide at pH 5.9. No intermediate steps of purification were taken and the overall yield was 30 % or more. Examples of the substituents included are carbohydrates, an enzyme inhibitor, a fumarate, and an acetate group. The introduction of different substituents into three individually addressable positions in a stepwise, efficient, and controllable reaction demonstrates that designed folded polypeptides are practically useful scaffolds that can be functionalized by using very simple chemistry in aqueous solution. Predicted applications include designed receptors, biosensors, and molecular devices.

The pH-dependent tertiary structure of a designed helix–loop–helix dimer

BACKGROUND De novo designed helix-loop-helix motifs can fold into well-defined tertiary structures if residues or groups of residues are incorporated at the helix-helix boundary to form helix-recognition sites that restrict the conformational degrees of freedom of the helical segments. Understanding the relationship between structure and function of conformational constraints therefore forms the basis for the engineering of non-natural proteins. This paper describes the design of an interhelical HisH+-Asp- hydrogen-bonded ion pair and the conformational stability of the folded helix-loop-helix motif. RESULTS GTD-C, a polypeptide with 43 amino acid residues, has been designed to fold into a hairpin helix-loop-helix motif that can dimerise to form a four-helix bundle. The folded motif is in slow conformational exchange on the NMR timescale and has a well-dispersed 1H NMR spectrum, a narrow temperature interval for thermal denaturation and a near-UV CD spectrum with some fine structure. The conformational stability is pH dependent with an optimum that corresponds to the pH for maximum formation of a hydrogen-bonded ion pair between HisH17+ in helix I and Asp27- in helix II. CONCLUSIONS The formation of an interhelical salt bridge is strongly suggested by the pH dependence of a number of spectroscopic probes to generate a well-defined tertiary structure in a designed helix-loop-helix motif. The thermodynamic stability of the folded motif is not increased by the formation of the salt bridge, but neighbouring conformations are destabilised. The use of this novel design principle in combination with hydrophobic interactions that provide sufficient binding energy in the folded structure should be of general use in de novo design of native-like proteins.