The human beta-defensin-3, an antibacterial peptide with multiple biological functions

Engineering antimicrobial peptides with improved antimicrobial and hemolytic activities

The rapid rise of antibiotic resistance in pathogens becomes a serious and growing threat to medicine and public health. Naturally occurring antimicrobial peptides (AMPs) are an important line of defense in the immune system against invading bacteria and microbial infection. In this work, we present a combined computational and experimental study of the biological activity and membrane interaction of the computationally designed Bac2A-based peptide library. We used the MARTINI coarse-grained molecular dynamics with adaptive biasing force method and the umbrella sampling technique to investigate the translocation of a total of 91 peptides with different amino acid substitutions through a mixed anionic POPE/POPG (3:1) bilayer and a neutral POPC bilayer, which mimic the bacterial inner membrane and the human red blood cell (hRBC) membrane, respectively. Potential of mean force (PMF, free energy profile) was obtained to measure the free energy barrier required to transfer the peptides from the bulk water phase to the water-membrane interface and to the bilayer interior. Different PMF profiles can indeed identify different membrane insertion scenarios by mapping out peptide-lipid energy landscapes, which are correlated with antimicrobial activity and hemolytic activity. Computationally designed peptides were further tested experimentally for their antimicrobial and hemolytic activities using bacteria growth inhibition assay and hemolysis assay. Comparison of PMF data with cell assay results reveals a good correlation of the peptides between predictive transmembrane activity and antimicrobial/hemolytic activity. Moreover, the most active mutants with the balanced substitutions of positively charged Arg and hydrophobic Trp residues at specific positions were discovered to achieve the improved antimicrobial activity while minimizing red blood cell lysis. Such substitutions provide more effective and cooperative interactions to distinguish the peptide interaction with different lipid bilayers. This work provides a useful computational tool to better understand the mechanism and energetics of membrane insertion of AMPs and to rationally design more effective AMPs.

Ficolin-1 is up-regulated in leukocytes and glomeruli from microscopic polyangiitis patients

Microscopic polyangiitis (MPA) is a systemic autoimmune disease that often has a fatal outcome. Although delineating the molecular pathogenesis is essential for its remedy, an understanding of its molecular mechanism has remained elusive. To search for new markers of active lesions that might help better understand the molecular basis of MPA and aid in its diagnosis, we here performed DNA microarray analysis with peripheral blood mononuclear cells (PBMCs). Compared to normal control, several genes were up- or down-regulated in MPA patients, including up-regulation of the mRNA level of ficolin-1 (FCN1 or M-ficolin), an innate pattern recognition complement molecule. The amount of ficolin-1, as detected by immunohistochemistry, was higher in the glomeruli of another group of MPA patients than in the glomeruli of control patients who harbored almost normal glomeruli. Many of the ficolin-1 dots were also positive for CD68, suggesting that the ficolin-1-positive cells were monocytes, such as macrophages or dendritic cells. This is not due to the difference in the number of neutrophil or monocytes in the blood samples of MPA and control patients. Taken together, we conclude that increased ficolin-1 expression could serve as a new marker for the characterization of MPA, especially when it is associated with local active lesions.

Snake venoms: attractive antimicrobial proteinaceous compounds for therapeutic purposes

Gram-positive and -negative bacteria are dangerous pathogens that may cause human infection diseases, especially due to the increasingly high prevalence of antibiotic resistance, which is becoming one of the most alarming clinical problems. In the search for novel antimicrobial compounds, snake venoms represent a rich source for such compounds, which are produced by specialized glands in the snake's jawbone. Several venom compounds have been used for antimicrobial effects. Among them are phospholipases A2, which hydrolyze phospholipids and could act on bacterial cell surfaces. Moreover, metalloproteinases and L-amino acid oxidases, which represent important enzyme classes with antimicrobial properties, are investigated in this study. Finally, antimicrobial peptides from multiple classes are also found in snake venoms and will be mentioned. All these molecules have demonstrated an interesting alternative for controlling microorganisms that are resistant to conventional antibiotics, contributing in medicine due to their differential mechanisms of action and versatility. In this review, snake venom antimicrobial compounds will be focused on, including their enormous biotechnological applications for drug development.

Diverse T-cell responses characterize the different manifestations of cutaneous graft-versus-host disease

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HCT) and can present in an acute (aGVHD), a chronic lichenoid (clGVHD), and a chronic sclerotic form (csGVHD). It is unclear whether similar or different pathomechanisms lead to these distinct clinical presentations. To address this issue, we collected lesional skin biopsies from aGVHD (n = 25), clGVHD (n = 17), and csGVHD (n = 7) patients as well as serial nonlesional biopsies from HCT recipients (prior to or post-HCT) (n = 14) and subjected them to phenotypic and functional analyses. Our results revealed striking differences between aGVHD and clGVHD. In aGVHD, we found a clear predominance of T helper (Th)2 cytokines/chemokines and, surprisingly, of interleukin (IL)-22 messenger RNA as well as an increase of IL-22-producing CD4(+) T cells. Thymic stromal lymphopoietin, a cytokine skewing the immune response toward a Th2 direction, was elevated at day 20 to 30 post-HCT in the skin of patients who later developed aGVHD. In sharp contrast to aGVHD, the immune response occurring in clGVHD showed a mixed Th1/Th17 signature with upregulated Th1/Th17 cytokine/chemokine transcripts and elevated numbers of interferon-γ- and IL-17-producing CD8(+) T cells. Our findings shed new light on the T-cell responses involved in the different manifestations of cutaneous GVHD and identify molecular signatures indicating the development of the disease.

C. albicans growth, transition, biofilm formation, and gene expression modulation by antimicrobial decapeptide KSL-W

Background

Antimicrobial peptides have been the focus of much research over the last decade because of their effectiveness and broad-spectrum activity against microbial pathogens. These peptides also participate in inflammation and the innate host defense system by modulating the immune function that promotes immune cell adhesion and migration as well as the respiratory burst, which makes them even more attractive as therapeutic agents. This has led to the synthesis of various antimicrobial peptides, including KSL-W (KKVVFWVKFK-NH₂), for potential clinical use. Because this peptide displays antimicrobial activity against bacteria, we sought to determine its antifungal effect on C. albicans. Growth, hyphal form, biofilm formation, and degradation were thus examined along with EFG1, NRG1, EAP1, HWP1, and SAP 2-4-5-6 gene expression by quantitative RT-PCR.

Results

This study demonstrates that KSL-W markedly reduced C. albicans growth at both early and late incubation times. The significant effect of KSL-W on C. albicans growth was observed beginning at 10 μg/ml after 5 h of contact by reducing C. albicans transition and at 25 μg/ml by completely inhibiting C. albicans transition. Cultured C. albicans under biofilm-inducing conditions revealed that both KSL-W and amphotericin B significantly decreased biofilm formation at 2, 4, and 6 days of culture. KSL-W also disrupted mature C. albicans biofilms. The effect of KSL-W on C. albicans growth, transition, and biofilm formation/disruption may thus occur through gene modulation, as the expression of various genes involved in C. albicans growth, transition and biofilm formation were all downregulated when C. albicans was treated with KSL-W. The effect was greater when C. albicans was cultured under hyphae-inducing conditions.

Conclusions

These data provide new insight into the efficacy of KSL-W against C. albicans and its potential use as an antifungal therapy.

The cytotoxic effect of magainin II on the MDA-MB-231 and M14K tumour cell lines

Many studies have highlighted the tumoricidal properties of some natural peptides known to have antimicrobial virtues. Also, the increasingly higher resistance to conventional antibiotics has become a global public health issue, and the need for new antibiotics has stimulated interest in finding and synthesizing new antimicrobial peptides, which may also be used as chemotherapeutic agents. Relying on the literature, the purpose of our in vitro research was to assess the tumoricidal potential of magainin II on a series of tumour cell lines, namely, MDA-MB-231 (breast adenocarcinoma) and M14K (human mesothelioma). The experimental results of our study revealed that the cytotoxic effects of magainin II depend on its concentration. Its efficiency is significant at 120 μM concentrations, and, although it is much lower, it persists even at 60 μM concentrations. The effects were insignificant at 30 μM concentrations. In our experimental research, the tumoricidal effect of magainin II was not significantly dependent on the type of tumour cell line used.

Properties and mechanisms of action of naturally occurring antifungal peptides

Antimicrobial peptides are a vital component of the innate immune system of all eukaryotic organisms and many of these peptides have potent antifungal activity. They have potential application in the control of fungal pathogens that are a serious threat to both human health and food security. Development of antifungal peptides as therapeutics requires an understanding of their mechanism of action on fungal cells. To date, most research on antimicrobial peptides has focused on their activity against bacteria. Several antimicrobial peptides specifically target fungal cells and are not active against bacteria. Others with broader specificity often have different mechanisms of action against bacteria and fungi. This review focuses on the mechanism of action of naturally occurring antifungal peptides from a diverse range of sources including plants, mammals, amphibians, insects, crabs, spiders, and fungi. While antimicrobial peptides were originally proposed to act via membrane permeabilization, the mechanism of antifungal activity for these peptides is generally more complex and often involves entry of the peptide into the cell.

Antibacterial efficacy of a human β-defensin-3 peptide on multispecies biofilms

INTRODUCTION

The aggregation of mixed bacterial flora into sessile biofilms on root canal surfaces can be one of the causes of persistent apical periodontitis. The aim of this study was to evaluate the antibacterial efficacy of human β-defensin-3 (HBD3) peptide on multispecies biofilms by using confocal laser scanning microscopy.

METHODS

Actinomyces naeslundii, Lactobacillus salivarius, Streptococcus mutans, and Enterococcus faecalis were cultured in a peptone-yeast-glucose broth, and their culture suspensions were combined in equal proportions. The mixed bacteria were inoculated on sterile coverslips placed into the wells of tissue culture plates to permit the formation of mixed species biofilm. After incubation for 3 weeks, the samples were treated for 24 hours with saline (control), saturated calcium hydroxide solution (CH), 2% chlorhexidine solution (CHX), and 50 μg/mL HBD3 solution. A commercial biofilm/viability assay kit was used to assess cell viability and analyze the 3-dimensional architecture of biofilms. The percentage of dead cells was determined from the ratio of biovolumes for the red subpopulation and the total biofilm.

RESULTS

Three medication groups showed a significant reduction of biovolume within the biofilms compared with the control group (P < .001). The HBD3-treated biofilms had a higher percentage of dead cells than the other medication groups (P < .05). The CH and CHX groups showed higher levels of bactericidal activity than saline (P < .05), and there was no significant difference between the 2 groups (P > .05).

CONCLUSIONS

HBD3 peptide exhibited more antibacterial activity against mature multispecies biofilms in vitro than either CH or CHX.

Identification, expression and bioactivity of Paramisgurnus dabryanus β-defensin that might be involved in immune defense against bacterial infection

β-defensins are a large family of multi-disulfide-bonded peptides with broad-spectrum antimicrobial activities that contribute to innate host defense in many organisms, but little information is available about β-defensins produced by freshwater fish lacking scales. We therefore cloned and identified a β-defensin gene from Chinese loach (Paramisgurnus dabryanus) by designing degenerate primers and using thermal asymmetric interlaced PCR. This gene is the first defensin gene ever identified in a non-scaled freshwater fish. Annotation of the protein domain architecture showed that the putative Chinese loach β-defensin contains the signature motif of six conserved cysteines within the mature peptide, an aspect similar to β-defensins of other marine fish. We also used quantitative real-time PCR to investigate the expression pattern of the Chinese loach β-defensin gene, mRNA of which could be observed in various tissues. After challenge with the pathogenic bacterium Aeromonas hydrophila, β-defensin expression was induced in the eye, gill, skin, and spleen of the adult loach. The bioactivity of the recombinant P. dabryanus β-defensin was examined against pathogenic bacteria, and the results suggest that this class 2 β-defensin has potential applications for treatment of bacterial infections.

Anti-bacterial activity of recombinant human β-defensin-3 secreted in the milk of transgenic goats produced by somatic cell nuclear transfer

The present study was conducted to determine whether recombinant human β-defensin-3 (rHBD3) in the milk of transgenic goats has an anti-bacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Streptococcus agalactiae (S. agalactiae) that could cause mastitis. A HBD3 mammary-specific expression vector was transfected by electroporation into goat fetal fibroblasts which were used to produce fourteen healthy transgenic goats by somatic cell nuclear transfer. The expression level of rHBD3 in the milk of the six transgenic goats ranged from 98 to 121 µg/ml at 15 days of lactation, and was maintained at 90–111 µg/ml during the following 2 months. Milk samples from transgenic goats showed an obvious inhibitory activity against E. coli, S. aureus and S. agalactiae in vitro. The minimal inhibitory concentrations of rHBD3 in milk against E. coli, S. aureus and S. agalactiae were 9.5–10.5, 21.8–23.0 and 17.3–18.5 µg/mL, respectively, which was similar to those of the HBD3 standard (P>0.05). The in vivo anti-bacterial activities of rHBD3 in milk were examined by intramammary infusion of viable bacterial inoculums. We observed that 9/10 and 8/10 glands of non-transgenic goats infused with S. aureus and E. coli became infected. The mean numbers of viable bacteria went up to 2.9×10³ and 95.4×10³ CFU/ml at 48 h after infusion, respectively; the mean somatic cell counts (SCC) in infected glands reached up to 260.4×10⁵ and 622.2×10⁵ cells/ml, which were significantly higher than the SCC in uninfected goat glands. In contrast, no bacteria was presented in glands of transgenic goats and PBS-infused controls, and the SSC did not significantly change throughout the period. Moreover, the compositions and protein profiles of milk from transgenic and non-transgenic goats were identical. The present study demonstrated that HBD3 were an effective anti-bacterial protein to enhance the mastitis resistance of dairy animals.

A site-specific recombinase-based method to produce antibiotic selectable marker free transgenic cattle

Antibiotic selectable marker genes have been widely used to generate transgenic animals. Once transgenic animals have been obtained, the selectable marker is no longer necessary but raises public concerns regarding biological safety. The aim of this study was to prepare competent antibiotic selectable marker free transgenic cells for somatic cell nuclear transfer (SCNT). PhiC31 intergrase was used to insert a transgene cassette into a "safe harbor" in the bovine genome. Then, Cre recombinase was employed to excise the selectable marker under the monitoring of a fluorescent double reporter. By visually tracking the phenotypic switch from red to green fluorescence, antibiotic selectable marker free cells were easily detected and sorted by fluorescence-activated cell sorting. For safety, we used phiC31 mRNA and cell-permeant Cre protein in this study. When used as donor nuclei for SCNT, these safe harbor integrated marker-free transgenic cells supported a similar developmental competence of SCNT embryos compared with that of non-transgenic cells. After embryo transfer, antibiotic selectable marker free transgenic cattle were generated and anti-bacterial recombinant human β-defensin-3 in milk was detected during their lactation period. Thus, this approach offers a rapid and safe alternative to produce antibiotic selectable marker free transgenic farm animals, thereby making it a valuable tool to promote the healthy development and welfare of transgenic farm animals.

Dependence of Alamethicin Membrane Orientation on the Solution Concentration

Alamethicin has been extensively studied as an antimicrobial peptide and is widely used as a simple model for ion channel proteins. It has been shown that the antimicrobial activity of peptides is related to their membrane orientation. In this study, we determined the relationship between the solution concentration of alamethicin and its membrane orientation in lipid bilayers using sum frequency generation (SFG) vibrational spectroscopy. Our SFG results indicated that the alamethicin molecules more or less lay down on the surface of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayers at a low peptide concentration of 0.84 μM; the α-helix segment tilts at about 88°, and 3₁₀-helix segment tilts at about 58° versus the surface normal. However, when the peptide concentration was increased to 15.6 μM, we observed that alamethicin molecules further inserted into the lipid bilayers: the α-helical component changes its orientation to make a 37° tilt from the lipid bilayer normal, and the 3₁₀-helical component tilts at about 50° versus the surface normal. This is in agreement with the barrel-stave mode for the alamethicin-cell membrane interaction as reported previously. Additionally, we have also studied membrane orientation of alamethicin as a function of peptide concentration with SFG. Our results showed that the membrane orientation of the alamethicin α-helical component changed substantially with the increase of the alamethicin concentration, while the membrane orientation of the 3₁₀-helical component remained more or less the same.

Differential expression of human beta defensin 2 and 3 in gastric mucosa of Helicobacter pylori-infected individuals

BACKGROUND

Antimicrobial peptides are key players of initial innate immune responses to human pathogens. Two major representatives, the human beta defensin 2 and 3 (hBD2 and hBD3), are both known to be regulated by, and to affect viability of, Helicobacter pylori. Previously, it was demonstrated in vitro that H. pylori actively abrogates hBD3 expression during prolonged infections. Here, we comprehensively assessed hBD2 and hBD3 expression ex vivo in the gastric mucosa of healthy individuals.

MATERIALS AND METHODS

Twenty volunteers (H. pylori positive and H. pylori negative: n = 10) were enrolled. Helicobacter pylori-positive subjects underwent eradication therapy and repeated the protocol. Expression of both defensins was assessed by quantitative RT-PCR and ELISA, and correlated with histopathologic degree of gastritis.

RESULTS

hBD2 and hBD3 were found to be ubiquitously expressed in all three groups. In general, hBD2 levels were elevated in relation to H. pylori infection (up to 40-fold). This upregulation correlated with degree of gastritis in corpus and antrum. In contrast, hBD3 protein levels were significantly decreased, while corresponding mRNA amounts remained unchanged. Eradication therapy led to normalization of mucosal hBD2 expression, while hBD3 expression demonstrated high interindividual variations among individuals.

CONCLUSIONS

Both defensins are ubiquitously but differentially expressed in gastric mucosa in relation to H. pylori infection. Ex vivo data support the notion that H. pylori infection is associated with reduced hBD3 expression in chronic active gastritis.

A technology for developing synbodies with antibacterial activity

The rise in antibiotic resistance has led to an increased research focus on discovery of new antibacterial candidates. While broad-spectrum antibiotics are widely pursued, there is evidence that resistance arises in part from the wide spread use of these antibiotics. Our group has developed a system to produce protein affinity agents, called synbodies, which have high affinity and specificity for their target. In this report, we describe the adaptation of this system to produce new antibacterial candidates towards a target bacterium. The system functions by screening target bacteria against an array of 10,000 random sequence peptides and, using a combination of membrane labeling and intracellular dyes, we identified peptides with target specific binding or killing functions. Binding and lytic peptides were identified in this manner and in vitro tests confirmed the activity of the lead peptides. A peptide with antibacterial activity was linked to a peptide specifically binding Staphylococcus aureus to create a synbody with increased antibacterial activity. Subsequent tests showed that this peptide could block S. aureus induced killing of HEK293 cells in a co-culture experiment. These results demonstrate the feasibility of using the synbody system to discover new antibacterial candidate agents.

Effect of repetitive lysine-tryptophan motifs on the eukaryotic membrane

In a previous study, we synthesized a series of peptides containing simple sequence repeats, (KW)_n–NH₂ (n = 2,3,4 and 5) and determined their antimicrobial and hemolytic activities, as well as their mechanism of antimicrobial action. However, (KW)₅ showed undesirable cytotoxicity against RBC cells. In order to identify the mechanisms behind the hemolytic and cytotoxic activities of (KW)₅, we measured the ability of these peptides to induce aggregation of liposomes. In addition, their binding and permeation activities were assessed by Trp fluorescence, calcein leakage and circular dichrorism using artificial phospholipids that mimic eukaryotic liposomes, including phosphatidylcholine (PC), PC/sphingomyelin (SM) (2:1, w/w) and PC/cholesterol (CH) (2:1, w/w). Experiments confirmed that only (KW)₅ induced aggregation of all liposomes; it formed much larger aggregates with PC:CH (2:1, w/w) than with PC or PC:SM (2:1, w/w). Longer peptide (KW)₅, but not (KW)₃ or (KW)₄, strongly bound and partially inserted into PC:CH compared to PC or PC:SM (2:1, w/w). Calcein release experiments showed that (KW)₅ induced calcein leakage from the eukaryotic membrane. Greater calcein leakage was induced by (KW)₅ from PC:CH than from PC:SM (2:1, w/w) or PC, whereas (KW)₄ did not induce calcein leakage from any of the liposomes. Circular dichroism measurements indicated that (KW)₅ showed higher conformational transition compared to (KW)₄ due to peptide-liposome interactions. Taken together, our results suggest that (KW)₅ reasonably mediates the aggregation and permeabilization of eukaryotic membranes, which could in turn explain why (KW)₅ displays efficient hemolytic activity.

Structural and functional studies on a proline-rich peptide isolated from swine saliva endowed with antifungal activity towards Cryptococcus neoformans

A proline-rich peptide of 2733Da, isolated from pig parotid granule preparations was tested against different pathogenic fungi. It showed interesting antifungal activity towards a clinical isolate of Cryptococcus neoformans, with an EC(50) of 2.2μM. Neither cytotoxic nor haemolytic effects were observed towards mammalian cells. Circular dichroism and infrared spectroscopic studies showed that the peptide adopted a combination of polyproline type-II, β-turn and unordered conformations at physiological temperatures. Temperature dependent experiments evidenced a tendency to adopt a polyproline-II helix conformation. From experiments with lipid vesicles, Neutral Red Uptake (NRU), haemolytic assays, and confocal microscopy studies, it could be hypothesized that the peptide may exert its antifungal effect by interacting with an intracellular target rather than through membrane damage.

Production of cloned embryos from caprine mammary epithelial cells expressing recombinant human β-defensin-3

Transgenic animals that express antimicrobial agents in their milk can inhibit bacterial pathogens that cause mastitis. Our objective was to produce human β-defensin-3 (HBD3) transgenic embryos by nuclear transfer using goat mammary epithelial cells (GMECs) as donor cells. Three GMEC lines (GMEC1, GMEC2, and GMEC3) were transfected with a HBD3 mammary-specific expression vector by electroporation. There was a difference (P < 0.05) in the rate of geneticin-resistant colony formation among cell lines GMEC1, GMEC2, and GMEC3 (39 and 47 vs. 19 colonies per 3 × 10(6) cells, respectively). After inducing expression, the mRNA and protein of HBD3 were detected by reverse transcription polymerase chain reaction and Western blot analysis in transgenic cells. Transgenic clonal cells expressing HBD3 were used as donor cells to investigate development of cloned embryos. There were no significant differences in rates of cleavage or blastocyst formation of cloned embryos from transgenic (GMEC1T2 and GMEC2T3) and nontransgenic (GMEC1 and GMEC2) GMECs (72.3 ± 5.0%, 69.5 ± 2.3%, 61.8 ± 4.8%, and 70.0 ± 2%; and 16.8 ± 0.5%, 17.5 ± 0.7%, 16.7 ± 0.9%, and 17.5 ± 0.6%, respectively). However, the fusion rate, cleavage rate, and blastocyst formation rate of cloned embryos from a transgenic clonal cell line (GMEC2T6, 50.7 ± 2.1%, 55.5 ± 2.0%, and 11.1 ± 0.6%) were lower than those of other groups (P < 0.05). We concluded that genetic modification of GMECs might not influence the in vitro development of cloned embryos, but that some of the transgenic clonal cells were not suitable for nuclear transfer to produce transgenic goats, because of low developmental rates. However, transgenic GMECs expressing HBD3 might be used as donor cells for producing transgenic goats that express increased concentrations of β-defensins in their milk.

Transplantation of BMSCs expressing hVEGF165 /hBD3 promotes wound healing in rats with combined radiation-wound injury

The combined radiation-wound injury is a refractory wound with decreased number or dysfunction of repairing cells and growth factors. This remains a challenge in clinical practice. The object of this study is to evaluate the therapeutic efficacy of a combination of human vascular endothelial growth factor 165 (hVEGF(165)) and human beta-defensin 3 (hBD3) in the treatment of such wounds. A plasmid-carrying hVEGF(165) gene and hBD3 gene was used to transfect rat bone-marrow-derived mesenchymal stem cells (BMSCs). The supernatant from the modified BMSCs significantly promoted the proliferation and cell migration of human endothelial cells and it also inhibited the growth of bacteria and fungus, demonstrating the successful expression of the transfected genes. The hVEGF(165)/hBD3-modified BMSCs were then injected into the sites of combined radiation-wound injury on rats. It demonstrated that wound-healing time was shortened significantly in the treated rats. The granulation tissue formation/maturation, skin appendage regeneration and collagen deposition were also improved significantly. Strong expression of hVEGF(165) and hBD3 was detected in the wound surface at early stage of the healing. The results indicate that topical transplantation of hVEGF(165)/hBD3-modified BMSCs promoted wound healing, and this gene therapy strategy presents a promising approach in the treatment of refractory wounds such as the combined radiation-wound injury.

Kinetic analysis and evaluation of the mechanisms involved in the resolution of experimental nontypeable Haemophilus influenzae-induced otitis media after transcutaneous immunization

Transcutaneous immunization (TCI) is a simple and needle-free method with which to induce protective immune responses. Using a chinchilla model of nontypeable Haemophilus influenzae (NTHI)-induced otitis media (OM), we examined the efficacy afforded by TCI with a novel chimeric immunogen called 'chimV4' which targets two critical adhesins expressed by NTHI, outer membrane protein P5 and the majority subunit of NTHI Type IV pilus, PilA. Experimental OM was first established in cohorts of animals, and then TCI performed via a therapeutic immunization regime by rubbing vaccine formulations on hydrated pinnae. The kinetics of resolution of established experimental disease was evaluated by clinically-relevant assessments of OM, bacterial culture of planktonic and adherent NTHI within the middle ear and gross examination of the relative amount of NTHI mucosal biofilms within the middle ear space. Within seven days after primary TCI, a significant reduction in the signs of OM, significantly fewer NTHI adherent to the middle ear mucosa and significant resolution of mucosal biofilms was detected in animals that received chimV4+ the adjuvant LT(R192G-L211A), compared to animals administered LT(R192G-L211A) alone or saline by TCI (p<0.05) with eradication of NTHI within an additional seven days. The mechanism for rapid disease resolution involved efflux of activated dermal dendritic cells from the pinnae after TCI, secretion of factors chemotactic for CD4(+) T-cells, induction of polyfunctional IFNγ- and IL-17-producing CD4(+) T-cells and secretion of host defense peptide within the middle ear. These data support TCI as a therapeutic intervention against experimental NTHI-induced OM and begin to elucidate the host response to immunization by this noninvasive regimen.

The Helicobacter pylori virulence effector CagA abrogates human β-defensin 3 expression via inactivation of EGFR signaling

Antimicrobial peptides are constituents of the first-line innate mucosal defense system that acts as a barrier to establishment of infection. The highly successful human gastric pathogen, Helicobacter pylori, is able to persistently colonize its host despite inducing expression of several antimicrobial peptides, including human β-defensin 3 (hBD3). We find that hBD3 is highly active against H. pylori in vitro and is rapidly induced during early infection via EGFR-dependent activation of MAP kinase and JAK/STAT signaling. However, during prolonged infection, hBD3 was subsequently downregulated by the H. pylori virulence determinant CagA. Upon translocation into host cells, CagA activated the cellular tyrosine phosphatase, SHP-2, terminating EGFR activation and downstream signaling and increasing bacterial viability. Chemical inhibition and knockdown of SHP-2 expression rescued hBD3 synthesis and bactericidal activity. Thus, we reveal how cagPAI-positive H. pylori strains use CagA to evade a key innate mucosal defense pathway to support the establishment of persistent infection.

Extracellular DNA within a nontypeable Haemophilus influenzae-induced biofilm binds human beta defensin-3 and reduces its antimicrobial activity

Biofilms formed by nontypeable Haemophilus influenzae (NTHI) are associated with multiple chronic infections of the airway, including otitis media. Extracellular DNA (eDNA) is part of the biofilm matrix and serves as a structural component. Human β-defensin-3 (hBD-3) is a cationic antimicrobial host defense protein (AMP) critical to the protection of the middle ear. We hypothesized that anionic eDNA could interact with and bind hBD-3 and thus shield NTHI in biofilms from its antimicrobial activity. We demonstrated that recombinant hBD-3 [(r)hBD-3] bound eDNA in vitro and that eDNA in biofilms produced by NTHI in the chinchilla middle ear co-localized with the orthologue of this AMP. Incubation of physiological concentrations of (r)hBD-3 with NTHI genomic DNA abrogated the ability of this innate immune effector to prevent NTHI from forming robust biofilms in vitro. Establishment of NTHI biofilms in the presence of both DNase I and (r)hBD-3 resulted in a marked reduction in the overall height and thickness of the biofilms and rescued the antimicrobial activity of the AMP. Our results demonstrated that eDNA in NTHI biofilms sequestered hBD-3 and thus diminished the biological activity of an important effector of innate immunity. Our observations have important implications for chronicity of NTHI-induced diseases.

Efficacy verification and microscopic observations of an anticancer peptide, CB1a, on single lung cancer cell

In this work, we introduce a new customized anti-lung cancer peptide, CB1a, with IC₅₀ of about 25.0 ± 1.6 μM on NCI-H460 lung cancer cells. Using a multi-cellular tumor spheroid (MCTS) model, results show that CB1a is potent in preventing the growth of lung cancer tumor-like growths in vitro. Additionally, atomic force microscopy (AFM) was used to examine cell surface damage of a single cancer. The mechanism for cell death under CB1a toxicity was verified as being largely due to cell surface damage. Moreover, with a treatment dosage of CB1a at 25 μM, Young's module (E) shows that the elasticity and stiffness of cancer cell decreased with time such that the interaction time for a 50% reduction of E (IT₅₀) was about 7.0min. This new single-cell toxicity investigation using IT₅₀ under AFM assay can be used to separately verify drug efficacy in support of the traditional IC₅₀ measurement in bulk solution. These results could be of special interest to researchers engaged in new drug development.

Human β-defensin-3 alters, but does not inhibit, the binding of Porphyromonas gingivalis haemagglutinin B to the surface of human dendritic cells

Human β-defensin-3 (HBD3) is a small, cationic, host defence peptide with broad antimicrobial activities and diverse innate immune functions. HBD3 binds to many microbial antigens and, in this study, we hypothesised that the known binding of HBD3 to Porphyromonas gingivalis recombinant haemagglutinin B (rHagB) alters, but does not inhibit, the binding of rHagB to human dendritic cells. To test this, human myeloid dendritic cells were incubated for 5 min with rHagB, HBD3 + rHagB (10:1 molar ratio), HBD3 or 0.1 M phosphate-buffered saline (PBS) (pH 7.2) and were then rapidly fixed and processed for confocal microscopy and ultramicrotomy. rHagB and HBD3 could be detected with primary monoclonal mouse antibody to rHagB (MoAb 1858) or polyclonal rabbit antibody to HBD3 (P241) and secondary fluorescent-labelled anti-mouse or anti-rabbit antibodies (confocal microscopy) or protein A-colloidal gold (immunoelectron microscopy). In cells incubated with rHagB only, fluorescence and protein A-colloidal gold were seen at the cell surface and throughout the cytoplasm. In cells incubated with HBD3+rHagB, fluorescence was observed only at the cell surface in a 'string of pearls' configuration. Overall, these results suggest that HBD3 binding to rHagB alters, but does not inhibit, the binding of rHagB to human myeloid dendritic cells.

The emerging role of peptides and lipids as antimicrobial epidermal barriers and modulators of local inflammation

Skin is complex and comprised of distinct layers, each layer with unique architecture and immunologic functions. Cells within these layers produce differing amounts of antimicrobial peptides and lipids (sphingoid bases and sebaceous fatty acids) that limit colonization of commensal and opportunistic microorganisms. Furthermore, antimicrobial peptides and lipids have distinct, concentration-dependent ancillary innate and adaptive immune functions. At 0.1-2.0 μM, antimicrobial peptides induce cell migration and adaptive immune responses to coadministered antigens. At 2.0-6.0 μM, they induce cell proliferation and enhance wound healing. At 6.0-12.0 μM, they can regulate chemokine and cytokine production and at their highest concentrations of 15.0-30.0 μM, antimicrobial peptides can be cytotoxic. At 1-100 nM, lipids enhance cell migration induced by chemokines, suppress apoptosis, and optimize T cell cytotoxicity, and at 0.3-1.0 μM they inhibit cell migration and attenuate chemokine and pro-inflammatory cytokine responses. Recently, many antimicrobial peptides and lipids at 0.1-2.0 μM have been found to attenuate the production of chemokines and pro-inflammatory cytokines to microbial antigens. Together, both the antimicrobial and the anti-inflammatory activities of these peptides and lipids may serve to create a strong, overlapping immunologic barrier that not only controls the concentrations of cutaneous commensal flora but also the extent to which they induce a localized inflammatory response.

DAMPD: a manually curated antimicrobial peptide database

The demand for antimicrobial peptides (AMPs) is rising because of the increased occurrence of pathogens that are tolerant or resistant to conventional antibiotics. Since naturally occurring AMPs could serve as templates for the development of new anti-infectious agents to which pathogens are not resistant, a resource that contains relevant information on AMP is of great interest. To that extent, we developed the Dragon Antimicrobial Peptide Database (DAMPD, http://apps.sanbi.ac.za/dampd) that contains 1232 manually curated AMPs. DAMPD is an update and a replacement of the ANTIMIC database. In DAMPD an integrated interface allows in a simple fashion querying based on taxonomy, species, AMP family, citation, keywords and a combination of search terms and fields (Advanced Search). A number of tools such as Blast, ClustalW, HMMER, Hydrocalculator, SignalP, AMP predictor, as well as a number of other resources that provide additional information about the results are also provided and integrated into DAMPD to augment biological analysis of AMPs.

EXPLORING THE ROLE OF C–H … π INTERACTIONS ON THE STRUCTURAL STABILITY OF ANTIMICROBIAL PEPTIDES

A computational analysis on the C – H … π interactions in a group of 53 antimicrobial peptides was investigated. A total of 162 C – H … π interactions were observed. Side-chain to side-chain C – H … π interactions are the predominant type of interactions in antimicrobial peptides data set. There was an average of one significant C – H … π interaction for every 7 residues in the antimicrobial peptides investigated. Long-range C – H … π interactions are the predominant type of interactions. The secondary structure preference, solvent accessibility and stabilization centers of these of C – H … π interacting residues were estimated. It is likely that the C – H … π interactions contribute significantly to the overall stability of antimicrobial peptides. These interactions were observed after a molecular dynamics study on these set of antimicrobial peptides using CHARMM force field.

Native thrombocidin-1 and unfolded thrombocidin-1 exert antimicrobial activity via distinct structural elements

Chemokines (chemotactic cytokines) can have direct antimicrobial activity, which is apparently related to the presence of a distinct positively charged patch on the surface. However, chemokines can retain antimicrobial activity upon linearization despite the loss of their positive patch, thus questioning the importance of this patch for activity. Thrombocidin-1 (TC-1) is a microbicidal protein isolated from human blood platelets. TC-1 only differs from the chemokine NAP-2/CXCL7 by a two-amino acid C-terminal deletion, but this truncation is crucial for antimicrobial activity. We assessed the structure-activity relationship for antimicrobial activity of TC-1. Reduction of the charge of the TC-1-positive patch by replacing lysine 17 with alanine reduced the activity against bacteria and almost abolished activity against the yeast Candida albicans. Conversely, augmentation of the positive patch by increasing charge density or size resulted in a 2-3-fold increased activity against Staphylococcus aureus, Escherichia coli, and Bacillus subtilis but did not substantially affect activity against C. albicans. Reduction of TC-1 resulted in loss of the folded conformation, but this disruption of the positive patch did not affect antimicrobial activity. Using overlapping 15-mer synthetic peptides, we demonstrate peptides corresponding to the N-terminal part of TC-1 to have similar antimicrobial activity as intact TC-1. Although we demonstrate that the positive patch is essential for activity of folded TC-1, unfolded TC-1 retained antimicrobial activity despite the absence of a positive patch. This activity is probably exerted by a linear peptide stretch in the N-terminal part of the molecule. We conclude that intact TC-1 and unfolded TC-1 exert antimicrobial activity via distinct structural elements.

Road to clinical efficacy: challenges and novel strategies for antimicrobial peptide development

Since the discovery of magainins, cecropins and defensins 30 years ago, antimicrobial peptides (AMPs) have been hailed as a potential solution to the dearth of novel antibiotic development. AMPs have shown robust activity against a wide variety of pathogens, including drug-resistant bacteria. Unlike small-molecule antibiotics, however, AMPs have failed to translate this success to the clinic. Only the polymyxins, gramicidins, nisin and daptomycin are currently approved for medical use; the latter is the only example to have been developed in the last several decades. Nonetheless, researchers continue to isolate, modify and develop novel AMPs for therapeutic applications. Efforts have focused on increasing stability, reducing cytotoxicity, improving antimicrobial activity and incorporating AMPs in novel formulations, including nanoscale particles. As peptide synthesis and recombinant production methodologies improve, and more relevant bioassays become available, it becomes increasingly likely that AMPs will break the regulatory barrier and enter the marketplace as valuable antimicrobial weapons in the next 10 years.

Antimicrobial peptides and proteins of the horse--insights into a well-armed organism

Antimicrobial peptides play a pivotal role as key effectors of the innate immune system in plants and animals and act as endogenous antibiotics. The molecules exhibit an antimicrobial activity against bacteria, viruses, and eukaryotic pathogens with different specificities and potencies depending on the structure and amino-acid composition of the peptides. Several antimicrobial peptides were comprehensively investigated in the last three decades and some molecules with remarkable antimicrobial properties have reached the third phase of clinical studies. Next to the peptides themselves, numerous organisms were examined and analyzed regarding their repertoire of antimicrobial peptides revealing a huge number of candidates with potencies and properties for future medical applications. One of these organisms is the horse, which possesses numerous peptides that are interesting candidates for therapeutical applications in veterinary medicine. Here we summarize investigations and knowledge on equine antimicrobial peptides, point to interesting candidates, and discuss prospects for therapeutical applications.

Cationic amphipathic peptides accumulate sialylated proteins and lipids in the plasma membrane of eukaryotic host cells

Cationic antimicrobial peptides (CAMPs) selectively target bacterial membranes by electrostatic interactions with negatively charged lipids. It turned out that for inhibition of microbial growth a high CAMP membrane concentration is required, which can be realized by the incorporation of hydrophobic groups within the peptide. Increasing hydrophobicity, however, reduces the CAMP selectivity for bacterial over eukaryotic host membranes, thereby causing the risk of detrimental side-effects. In this study we addressed how cationic amphipathic peptides—in particular a CAMP with Lysine–Leucine–Lysine repeats (termed KLK)—affect the localization and dynamics of molecules in eukaryotic membranes. We found KLK to selectively inhibit the endocytosis of a subgroup of membrane proteins and lipids by electrostatically interacting with negatively charged sialic acid moieties. Ultrastructural characterization revealed the formation of membrane invaginations representing fission or fusion intermediates, in which the sialylated proteins and lipids were immobilized. Experiments on structurally different cationic amphipathic peptides (KLK, 6-MO-LF11-322 and NK14-2) indicated a cooperation of electrostatic and hydrophobic forces that selectively arrest sialylated membrane constituents.

The synthetic peptides bovine enteric β-defensin (EBD), bovine neutrophil β-defensin (BNBD) 9 and BNBD 3 are chemotactic for immature bovine dendritic cells

Human and murine immature DCs (iDCs) are highly efficient in antigen capture and processing, while as mature cells they present antigen and are potent initiators of cell-mediated immune responses. Consequently, iDCs are logical targets for vaccine antigens. Originally discovered for their antimicrobial activity, and thought of as strictly part of the innate immune system, studies with defensins such as human β (beta)-defensin 2 (hBD2) and murine β-defensin 2 (mBD2) have shown that they can function as chemo-attractant for iDCs and, in vaccination strategies, can enhance antigen-specific adaptive immune responses. Most studies to date have been conducted in mice. In contrast, little is known about defensins in cattle. To expand our understanding of the role of defensins in modulating immune responses in cattle, DCs were generated from bovine monocytes and the immature state of these bovine DCs was characterized phenotypically and through functional assays. By day 3 (DC3), bovine monocyte-derived DCs stained positively for DC-specific receptors CD1, CD80/86, CD205, DC-Lamp and MMR. When compared to conventional 6-day DC cultures or DCs cultured for 10 days with and without maturation factors, these DC3 were functionally at their most immature stage. Fourteen of the 16 known bovine β-defensins were synthesized and the synthetic peptides were screened for their ability to attract bovine iDCs. Bovine DC3 were consistently attracted to BNBD3, an analog of BNBD3 (aBNBD3), BNBD9 and bovine EBD in vitro and to aBNBD3 in vivo. These results are the first to describe chemotactic ability of synthetic bovine β-defensins for immature bovine monocyte-derived DCs.

Using fluorine nuclear magnetic resonance to probe changes in the structure and dynamics of membrane-active peptides interacting with lipid bilayers

The antimicrobial peptide MSI-78 serves as a model system for studying interactions of bioactive peptides with membranes. Using a series of MSI-78 peptides that incorporate l-4,4,4-trifluoroethylglycine, a small and sensitive (19)F nuclear magnetic resonance probe, we investigated how the local structure and dynamics of the peptide change when it binds to the lipid bilayer. The fluorinated MSI-78 analogues exhibited position-specific changes in (19)F chemical shift ranging from 1.28 to -1.35 ppm upon binding to lipid bicelles. The largest upfield shifts are associated with the most hydrophobic positions in the peptide. Changes in solvent isotope effects (H(2)O/D(2)O) on (19)F chemical shifts were observed for the peptides that are consistent with the MSI-78 solvent-inaccessible hydrophobic core upon binding bicelles. Transverse relaxation measurements of the (19)F nucleus, using the Carr-Purcell-Meiboom-Gill pulse sequence, were used to examine changes in the local mobility of MSI-78 that occur upon binding to the lipid bilayer. Positions in the hydrophobic core of peptide-membrane complex show the greatest decrease in mobility upon binding of the lipid bilayer, whereas residues that interact with lipid headgroups are more mobile. The most mobile positions are at the N- and C-termini of the peptide. These results provide support for the proposed mechanism of membrane disruption by MSI-78 and reveal new details about the dynamic changes that accompany membrane binding.

Expression of plectasin in Pichia pastoris and its characterization as a new antimicrobial peptide against Staphyloccocus and Streptococcus

Recombinant plectasin, the first fungus defensin, was expressed in Pichia pastoris and purified, and its physical, chemical and antimicrobial characteristics were studied. Following a 120 h induction of recombinant yeast, the amount of total secreted protein reached 748.63 μg/ml. The percentage of recombinant plectasin was estimated to be 71.79% of the total protein. After purification with a Sephadex G-25 column and RP-HPLC, the identity of plectasin was verified by MALDI-TOF MS. Plectasin exhibited strong antimicrobial activity against the Gram-positive bacteria Staphyloccocusaureus, Staphylococcus epidermidis, Streptococcus pneumoniae, and Streptococcus suis. At a concentration of 2560 μg/ml, this peptide showed approximately equal activity against S. aureus, S. epidermidis, S. suis, and S. pneumoniae, when compared to 320 μg/ml vancomycin, 640 μg/ml penicillin, 320 μg/ml vancomycin and 160 μg/ml vancomycin, respectively. In addition, plectasin showed anti-S. aureus activity over a wide pH range of 2.0 and 10.0, a high thermal stability at 100 °C for 1h and remarkable resistance to papain and pepsin. The expression and characterization of recombinant plectasin in P. pastoris has potential to treat Streptococcus and Staphyloccocus infections when most traditional antibiotics show no effect on them. Our results indicate that plectasin can be produced in large quantities, and that it has pharmaceutical importance for the prevention and clinical treatment of Staphyloccocus and Streptococcus infections.

Effect of human beta-defensin-3 on the proliferation of fibroblasts on periodontally involved root surfaces

Human beta-defensin-3 (HBD-3) has versatile antibacterial activity against oral bacteria and can promote the proliferation of fibroblasts. The goal of the present study was to investigate the effect of HBD-3 on attachment and proliferation of periodontal ligament cells (PDL) onto the periodontitis affected root surfaces. PDL cells were seeded onto healthy and diseased root specimens with scaling and root planing (SRP), SRP & HBD-3 (100 ng/ml), or SRP & HBD-3 (200 ng/ml) treatment for 1, 3, and 7 days incubation. The results showed that HBD-3, especially in the 200 ng/ml group, significantly promoted fibroblast attachment and proliferation onto the diseased root surfaces. The cell number in the HBD-3 group was much greater than in the group treated with SRP alone. On day 7, the cells in the HBD-3 were well-spread and formed a network similar to those on the surfaces of the healthy root specimens. These results suggest that HBD-3 could play an important role in antibacterial activity and fibroblast proliferation, thus promoting periodontal regeneration. Meanwhile, HBD-3 might act as a potent regeneration-promoter in infectious diseases.

Structural studies of a peptide with immune modulating and direct antimicrobial activity

The structure and function of the synthetic innate defense regulator peptide 1018 was investigated. This 12 residue synthetic peptide derived by substantial modification of the bovine cathelicidin bactenecin has enhanced innate immune regulatory and moderate direct antibacterial activities. The solution state NMR structure of 1018 in zwitterionic dodecyl phosphocholine (DPC) micelles indicated an α-helical conformation, while secondary structures, based on circular dichroism measurements, in anionic sodium dodecyl sulfate (SDS) and phospholipid vesicles (POPC/PG in a 1:1 molar ratio) and simulations revealed that 1018 can adopt a variety of folds, tailored to its different functions. The structural data are discussed in light of the ability of 1018 to potently induce chemokine responses, suppress the LPS-induced TNF-α response, and directly kill both Gram-positive and Gram-negative bacteria.

Limiting an antimicrobial peptide to the lipid-water interface enhances its bacterial membrane selectivity: a case study of MSI-367

In a minimalist design approach, a synthetic peptide MSI-367 [(KFAKKFA)(3)-NH(2)] was designed and synthesized with the objective of generating cell-selective nonlytic peptides, which have a significant bearing on cell targeting. The peptide exhibited potent activity against both bacteria and fungi, but no toxicity to human cells at micromolar concentrations. Bacterial versus human cell membrane selectivity of the peptide was determined via membrane permeabilization assays. Circular dichroism investigations revealed the intrinsic helix propensity of the peptide, β-turn structure in aqueous buffer and extended and turn conformations upon binding to lipid vesicles. Differential scanning calorimetry experiments with 1,2-dipalmitoleoyl-sn-glycero-3-phosphatidylethanolamine bilayers indicated the induction of positive curvature strain and repression of the fluid lamellar to inverted hexagonal phase transition by MSI-367. Results of isothermal titration calorimetry (ITC) experiments suggested the possibility of formation of specific lipid-peptide complexes leading to aggregation. (2)H nuclear magnetic resonance (NMR) of deuterated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) multilamellar vesicles confirmed the limited effect of the membrane-embedded peptide at the lipid-water interface. (31)P NMR data indicated changes in the lipid headgroup orientation of POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylethanolamine lipid bilayers upon peptide binding. Membrane-embedded and membrane-inserted states of the peptide were observed via sum frequency generation vibrational spectroscopy. Circular dichroism, ITC, and (31)P NMR data for Escherichia coli lipids agree with the hypothesis that strong electrostatic lipid-peptide interactions embrace the peptide at the lipid-water interface and provide the basis for bacterial cell selectivity.

Structure, interactions, and antibacterial activities of MSI-594 derived mutant peptide MSI-594F5A in lipopolysaccharide micelles: role of the helical hairpin conformation in outer-membrane permeabilization

Lipopolysaccharide (LPS) provides a well-organized permeability barrier at the outer membrane of Gram-negative bacteria. Host defense cationic antimicrobial peptides (AMPs) need to disrupt the outer membrane before gaining access to the inner cytoplasmic membrane or intracellular targets. Several AMPs are largely inactive against Gram-negative pathogens due to the restricted permeation through the LPS layer of the outer membrane. MSI-594 (GIGKFLKKAKKGIGAVLKVLTTG) is a highly active AMP with a broad-spectrum of activities against bacteria, fungi, and virus. In the context of LPS, MSI-594 assumes a hairpin helical structure dictated by packing interactions between two helical segments. Residue Phe5 of MSI-594 has been found to be engaged in important interhelical interactions. In order to understand plausible structural and functional inter-relationship of the helical hairpin structure of MSI-594 with outer membrane permeabilization, a mutant peptide, termed MSI-594F5A, containing a replacement of Phe5 with Ala has been prepared. We have compared antibacterial activities, outer and inner membrane permeabilizations, LPS binding affinity, perturbation of LPS micelles structures by MSI-594 and MSI-594F5A peptides. Our results demonstrated that the MSI-594F5A has lower activities against Gram-negative bacteria, due to limited permeabilization through the LPS layer, however, retains Gram-positive activity, akin to MSI-594. The atomic-resolution structure of MSI-594F5A has been determined in LPS micelles by NMR spectroscopy showing an amphipathic curved helix without any packing interactions. The 3D structures, interactions, and activities of MSI-594 and its mutant MSI-594F5A in LPS provide important mechanistic insights toward the requirements of LPS specific conformations and outer membrane permeabilization by broad-spectrum antimicrobial peptides.

The structural parameters for antimicrobial activity, human epithelial cell cytotoxicity and killing mechanism of synthetic monomer and dimer analogues derived from hBD3 C-terminal region

Understanding the molecular mechanisms of antimicrobial peptide-membrane interactions is crucial in predicting the design of useful synthetic antimicrobial peptide analogues. Defensins are small (3-5 kDa) cysteine-rich cationic proteins which constitute the front line of host innate immunity. In this study, a series of eight 10 AA C-terminal analogues of hBD3 [sequence: RGRKXXRRKK, X = W, F, Y, V, L, I, H, C(Acm); net charge = +7, coded as W2, F2, Y2, V2, L2, I2, H2, and C2] and covalent V2-dimer [(RGRKVVRR)(2)KK] (18 AA, net charge = +11) were synthesized using solid phase peptide synthesis (SPPS) in Fmoc chemistry. Wild-type hBD3 was used as a control in all analyses. W2, V2, and especially Y2 showed high activity selectively against Gram-negative bacteria Pseudomonas aeruginosa in the concentration range of 4.3-9.7 microM. The covalent dimeric form of V2-monomer, V2-dimer, showed increased antibacterial killing compared to the monomeric form, V2-monomer. Cytotoxicity assays on a human conjunctival epithelial cell line (IOBA-NHC cells) showed that no change in viable cell number 24 h after constant exposure to all the eight peptide analogues even at concentrations up to 200 microg/ml. Fluorescence correlation spectroscopy (FCS) was used to study the interaction of these peptides against POPC vesicles (neutral; mammalian cell membrane mimic) and POPG vesicles (negatively charged; bacterial cell membrane mimic). Using FCS, significant aggregation and some leakage of Rhodamine dye were observed with POPG with Y2, W2 and V2 at the concentration of 5-10 mmicroM and no significant aggregation or disruption of vesicles was observed for all peptide analogues tested against POPC. V2-dimer induced more leakage and aggregation than the monomeric form. Overall, V2-dimer is the most effective antimicrobial peptide, with aggregation of POPG vesicles observed at concentrations as low as 1 microM. The concentration of 5-10 microM for Y2 from FCS correlated with the concentration of 5 microM (6.25 microg/ml), at which Y2 showed a cooperative increase in the activity. This suggests a structural transition of Y2 in the 2.5-5 microM concentration range resulting in the correlated increased antimicrobial activity. These results and the FCS together with previous NMR and molecular dynamics (MD) suggested that the charge density-based binding affinity, stable covalent dimerization, the ability to dimerize or even oligomerize and adopt a well-defined structure are important physicochemical properties distinguishing more effective cationic antimicrobial peptides.

Skin bacteria after chlorhexidine exposure-is there a difference in response to human beta-Defensin-3?

We investigated whether exposure to sub-lethal concentrations of chlorhexidine digluconate (CHG) changed the response of five Staphylococcus spp. to human beta-Defensin-3 (hBD-3). The change in response for each strain was determined in vitro with time-kill experiments in suspension by comparing the mean log(10) reduction caused by hBD-3 at 1.5 and 3 h in exposed and non-exposed bacteria. The identity of staphylococcal species was verified by DNA sequence homology in the gyrA genes in comparison with reference strains. Baseline sub-lethal concentrations allowing visible bacterial growth were between 0.0625 and 0.25 microg/ml. Sub-lethal CHG concentrations increased within 3 days in two isolates. For S. capitis 19/2, CHG-exposed cells were less susceptible to 0.5 microg/ml hBD-3 (log(10) reduction 0.78 versus 2.06 at 1.5 h; p < 0.001; t-test). For S. aureus, however, CHG-exposed cells were more susceptible to 1 microg/ml hBD-3. The observed changes between CHG-exposed and non-exposed cells did not indicate a general trend in response to hBD-3. Overall, we found no consistent evidence that 3 days of exposure to CHG changed the response of five Staphylococcus spp. to hBD-3. The use of CHG for skin antisepsis is, based on our data, unlikely to change the natural defence activity of hBD-3.

Isoleucine/leucine2 is essential for chemoattractant activity of beta-defensin Defb14 through chemokine receptor 6

Beta-defensins are both antimicrobial and able to chemoattract various immune cells including immature dendritic cells and CD4 T cells through CCR6. They are short, cationic peptides with a highly conserved six-cysteine motif. It has been shown that only the fifth cysteine is critical for chemoattraction of cells expressing CCR6. In order to identify other residues essential for functional interaction with CCR6 we used a library of peptide deletion derivatives based on Defb14. Loss of the initial two amino acids from the Defb14-1C(V) derivative destroys its ability to chemoattract cells expressing CCR6. As the second amino acid is an evolutionarily conserved leucine, we make full-length Defb14-1C(V) peptides with substitution of the leucine(2) for glycine (L2G), lysine (L2K) or isoleucine (L2I). Defb14-1C(V) L2G and L2K and are unable to chemoattract CCR6 expressing cells but the semi-conservative change L2I has activity. By circular dichroism spectroscopy we can see no evidence for a significant change in secondary structure as a consequence of these substitutions and so cannot attribute loss of chemotactic activity with disruption of the N-terminal helix. We conclude that isoleucine/leucine in the N-terminal alpha-helix region of this beta-defensin is essential for CCR6-mediated chemotaxis.