Menstrual hemocidin HbB115-146 is an acidophilic antibacterial peptide potentiating the activity of human defensins, cathelicidin and lysozyme

Bioinformatic Analysis of the Wound Peptidome Reveals Potential Biomarkers and Antimicrobial Peptides

Wound infection is a common and serious medical condition with an unmet need for improved diagnostic tools. A peptidomic approach, aided by mass spectrometry and bioinformatics, could provide novel means of identifying new peptide biomarkers for wound healing and infection assessment. Wound fluid is suitable for peptidomic analysis since it is both intimately tied to the wound environment and is readily available. In this study we investigate the peptidomes of wound fluids derived from surgical drainages following mastectomy and from wound dressings following facial skin grafting. By applying sorting algorithms and open source third party software to peptidomic label free tandem mass spectrometry data we provide an unbiased general methodology for analyzing and differentiating between peptidomes. We show that the wound fluid peptidomes of patients are highly individualized. However, differences emerge when grouping the patients depending on wound type. Furthermore, the abundance of peptides originating from documented antimicrobial regions of hemoglobin in infected wounds may contribute to an antimicrobial wound environment, as determined by in silico analysis. We validate our findings by compiling literature on peptide biomarkers and peptides of physiological significance and cross checking the results against our dataset, demonstrating that well-documented peptides of immunological significance are abundant in infected wounds, and originate from certain distinct regions in proteins such as hemoglobin and fibrinogen. Ultimately, we have demonstrated the power using sorting algorithms and open source software to help yield insights and visualize peptidomic data.

Novel haemoglobin-derived antimicrobial peptides from chicken (Gallus gallus) blood: purification, structural aspects and biological activity

AIM

To purify and characterize antimicrobial peptides derived from the acid extract of Gallus gallus blood cells.

METHODS AND RESULTS

Two polypeptides (i.e. CHb-1 and CHb-2) with antibacterial activity were detected in the acidic extract of blood cells from chicken (G. gallus). The isolated peptides that possessed a potent antibacterial activity were purified using a two-step chromatography procedure that involved solid-phase extraction of a total protein/peptide extract followed by thin fractionation by reversed-phase high performance liquid chromatography (RP-HPLC). The molecular masses of the purified peptides were similar and were 4824·4 and 4825·2 Da, which have been measured by matrix-assisted laser desorption/ionization mass spectrometry (MALDI TOF MS). Their amino acid sequences were determined by Edman degradation and showed that the peptides were fully identical to the two fragments of G. gallus α-haemoglobin localized into different subunits (A and D respectively). The peptides were active in micromolar concentrations against Gram-negative Escherichia coli K12 TG1. Using the 1-N-phenylnaphthylamine, the FITC-dextran labelled probes and the live/dead staining allowed to show the hemocidin mode of action and estimate the pore size.

CONCLUSION

In this study, for the first time, α-haemoglobin from chicken (G. gallus) has been investigated as a donor of the two high homologous native peptide fragments that possess potent antibacterial activity in vitro. These are membrane-active peptides and their mechanism of action against E. coli involves a toroidal pore formation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The obtained results expand the perception of the role of haemoglobin in a living system, describing it as a source of multifunction substances. Additionally, the data presented in this paper may contribute to the development of new, cost-effective, antimicrobial agents.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era.

Immunological properties of oxygen-transport proteins: hemoglobin, hemocyanin and hemerythrin

It is now well documented that peptides with enhanced or alternative functionality (termed cryptides) can be liberated from larger, and sometimes inactive, proteins. A primary example of this phenomenon is the oxygen-transport protein hemoglobin. Aside from respiration, hemoglobin and hemoglobin-derived peptides have been associated with immune modulation, hematopoiesis, signal transduction and microbicidal activities in metazoans. Likewise, the functional equivalents to hemoglobin in invertebrates, namely hemocyanin and hemerythrin, act as potent immune effectors under certain physiological conditions. The purpose of this review is to evaluate the true extent of oxygen-transport protein dynamics in innate immunity, and to impress upon the reader the multi-functionality of these ancient proteins on the basis of their structures. In this context, erythrocyte-pathogen antibiosis and the immune competences of various erythroid cells are compared across diverse taxa.

An improved 96-well turbidity assay for T4 lysozyme activity

T4 lysozyme (T4L) is an important model system for investigating the relationship between protein structure and function. Despite being extensively studied, a reliable, quantitative activity assay for T4L has not been developed. Here, we present an improved T4L turbidity assay as well as an affinity-based T4L expression and purification protocol. This assay is designed for 96-well format and utilizes conditions amenable for both T4L and other lysozymes. This protocol enables easy, efficient, and quantitative characterization of T4L variants and allows comparison between different lysozymes. Our method:

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Is applicable for all lysozymes, with enhanced sensitivity for T4 lysozyme compared to other 96-well plate turbidity assays;

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Utilizes standardized conditions for comparing T4 lysozyme variants and other lysozymes; and

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Incorporates a simplified expression and purification protocol for T4 lysozyme.

HbAHP-25, an In-Silico Designed Peptide, Inhibits HIV-1 Entry by Blocking gp120 Binding to CD4 Receptor

Human Immunodeficiency Virus (HIV-1) poses a serious threat to the developing world and sexual transmission continues to be the major source of new infections. Therefore, the development of molecules, which prevent new HIV-1 infections, is highly warranted. In the present study, a panel of human hemoglobin (Hb)-α subunit derived peptides and their analogues, with an ability to bind gp120, were designed in-silico and their anti-HIV-1 activity was evaluated. Of these peptides, HbAHP-25, an analogue of Hb-α derived peptide, demonstrated significant anti-HIV-1 activity. HbAHP-25 was found to be active against CCR5-tropic HIV-1 strains (ADA5 and BaL) and CXCR4-tropic HIV-1 strains (IIIB and NL4-3). Surface plasmon resonance (SPR) and ELISA revealed direct interaction between HbAHP-25 and HIV-1 envelope protein, gp120. The peptide prevented binding of CD4 to gp120 and blocked subsequent steps leading to entry and/or fusion or both. Anti-HIV activity of HbAHP-25 appeared to be specific as it failed to inhibit the entry of HIV-1 pseudotyped virus (HIV-1 VSV). Further, HbAHP-25 was found to be non-cytotoxic to TZM-bl cells, VK2/E6E7 cells, CEM-GFP cells and PBMCs, even at higher concentrations. Moreover, HbAHP-25 retained its anti-HIV activity in presence of seminal plasma and vaginal fluid. In brief, the study identified HbAHP-25, a novel anti-HIV peptide, which directly interacts with gp120 and thus has a potential to inhibit early stages of HIV-1 infection.

Antimicrobial function of SHβAP, a novel hemoglobin β chain-related antimicrobial peptide, isolated from the liver of skipjack tuna, Katsuwonus pelamis

A 2.3 kDa of antimicrobial peptide was purified from an acidified liver extract of skipjack tuna, Katsuwonus pelamis, by preparative acid-urea-polyacrylamide gel electrophoresis and C18 reversed-phase HPLC. A comparison of the amino acid sequence of the purified peptide with those of other known polypeptides revealed high homology with the C-terminus of hemoglobin β-chain; thus, this peptide was designated as the Skipjack Hemoglobin β chain-related Antimicrobial Peptide (SHβAP). SHβAP showed potent antimicrobial activity against Gram-positive bacteria, such as Bacillus subtilis, Staphylococcus aureus, and Streptococcus iniae (minimal effective concentrations [MECs], 6.5-57.0 μg/mL), Gram-negative bacteria, such as Escherichia coli D31, Pseudomonas aeruginosa, Salmonella enterica, Shigella sonnei, and two Vibrio parahaemolyticus species (MECs, 2.0-19.0 μg/mL), and against Candida albicans (MEC; 12.0 μg/mL) without significant hemolytic activity. Antimicrobial activity of this peptide was heatstable and pH resistant but is sensitive to proteases and salt. SHβAP did not show membrane permeabilization and killing ability. The secondary structural prediction and the homology modeling expected that this peptide formed an amphipathic α-helical structure. This is the first report the purification of a novel antimicrobial peptide related to the C-terminus of hemoglobin β-chain from marine fish.

Chemerin is an antimicrobial agent in human epidermis

Chemerin, a chemoattractant ligand for chemokine-like receptor 1 (CMKLR1) is predicted to share similar tertiary structure with antibacterial cathelicidins. Recombinant chemerin has antimicrobial activity. Here we show that endogenous chemerin is abundant in human epidermis, and that inhibition of bacteria growth by exudates from organ cultures of primary human skin keratinocytes is largely chemerin-dependent. Using a panel of overlapping chemerin-derived synthetic peptides, we demonstrate that the antibacterial activity of chemerin is primarily mediated by Val⁶⁶-Pro⁸⁵, which causes direct bacterial lysis. Therefore, chemerin is an antimicrobial agent in human skin.

Purification and characterization of Hb 98-114: a novel hemoglobin-derived antimicrobial peptide from the midgut of Rhipicephalus (Boophilus) microplus

The antimicrobial activity of hemoglobin fragments (hemocidins) has been reported in a variety of models. The cattle tick Rhipicephalus (Boophilus) microplus is a blood sucking arthropod from where the first in vivo-generated hemocidin was characterized (Hb 33-61). In the present work we identified a novel antimicrobial peptide from the midgut of fully engorged R. (B.) microplus females, which comprises the amino acids 98-114 of the alpha subunit of bovine hemoglobin, and was designated Hb 98-114. This peptide was active against several yeast and filamentous fungi, although no activity was detected against bacteria up to 50μM of the synthetic peptide. Hb 98-114 was capable of permeabilizing Candida albicans cell membrane and had a fungicidal effect against this yeast. Circular dichroism (CD) and nuclear magnetic resonance (NMR) experiments showed that Hb 98-114 has a random conformation in aqueous solution but switches to an alpha-helical conformation in the presence of sodium dodecyl sulfate (SDS). This alpha helix adopts an amphipathic structure which may be the mechanism of cell membrane permeabilization. Importantly, Hb 98-114 may play an important role in defending the tick midgut against fungal pathogens and is the first hemocidin with specific antifungal activity to be characterized.

Synergistic action of Galleria mellonella anionic peptide 2 and lysozyme against Gram-negative bacteria

Lysozyme and antimicrobial peptides are key factors of the humoral immune response in insects. In the present work lysozyme and anionic defense peptide (GMAP2) were isolated from the hemolymph of the greater wax moth Galleria mellonella and their antibacterial activity was investigated. Adsorption of G. mellonella lysozyme on the cell surface of Gram-positive and Gram-negative bacteria was demonstrated using immunoblotting with anti-G. mellonella lysozyme antibodies. Lysozyme effectively inhibited the growth of selected Gram-positive bacteria, which was accompanied by serious alterations of the cell surface, as revealed by atomic force microscopy (AFM) imaging. G. mellonella lysozyme used in concentrations found in the hemolymph of naive and immunized larvae, perforated also the Escherichia coli cell membrane and the level of such perforation was considerably increased by GMAP2. GMAP2 used alone did not perforate E. coli cells nor influence lysozyme muramidase activity. However, the peptide induced a decrease in the turgor pressure of the bacterial cell. Moreover, in the samples of bacteria treated with a mixture of lysozyme and GMAP2 the sodium chloride crystals were found, suggesting disturbance of ion transport across the membrane leading to cell disruption. These results clearly indicated the synergistic action of G. mellonella lysozyme and anionic peptide 2 against Gram-negative bacteria. The reported results suggested that, thanks to immune factors constitutively present in hemolymph, G. mellonella larvae are to some extent protected against infection caused by Gram-negative bacteria.

Enhanced leishmanicidal activity of cryptopeptide chimeras from the active N1 domain of bovine lactoferrin

Two antimicrobial cryptopeptides from the N1 domain of bovine lactoferrin, lactoferricin (LFcin17-30) and lactoferrampin (LFampin265-284), together with a hybrid version (LFchimera), were tested against the protozoan parasite Leishmania. All peptides were leishmanicidal against Leishmania donovani promastigotes, and LFchimera showed a significantly higher activity over its two composing moieties. Besides, it was the only peptide active on Leishmania pifanoi axenic amastigotes, already showing activity below 10 μM. To investigate their leishmanicidal mechanism, promastigote membrane permeabilization was assessed by decrease of free ATP levels in living parasites, entrance of the vital dye SYTOX Green (MW = 600 Da) and confocal and transmission electron microscopy. The peptides induced plasma membrane permeabilization and bioenergetic collapse of the parasites. To further clarify the structural traits underlying the increased leishmanicidal activity of LFchimera, the activity of several analogues was assessed. Results revealed that the high activity of these hybrid peptides seems to be related to the order and sequence orientation of the two cryptopeptide moieties, rather than to their particular linkage through an additional lysine, as in the initial LFchimera. The incorporation of both antimicrobial cryptopeptide motifs into a single linear sequence facilitates chemical synthesis and should help in the potential clinical application of these optimized analogues.

On the selectivity and efficacy of defense peptides with respect to cancer cells

Here, we review potential determinants of the anticancer efficacy of innate immune peptides (ACPs) for cancer cells. These determinants include membrane-based factors, such as receptors, phosphatidylserine, sialic acid residues, and sulfated glycans, and peptide-based factors, such as residue composition, sequence length, net charge, hydrophobic arc size, hydrophobicity, and amphiphilicity. Each of these factors may contribute to the anticancer action of ACPs, but no single factor(s) makes an overriding contribution to their overall selectivity and toxicity. Differences between the anticancer actions of ACPs seem to relate to different levels of interplay between these peptide and membrane-based factors.

Expression of HMGB1 and HMGN2 in gingival tissues, GCF and PICF of periodontitis patients and peri-implantitis

High mobility group chromosomal protein B1 (HMGB1) and N2 (HMGN2), two members of High mobility group (HMG) family, play important role in inflammation. The purposes of this study were to investigate the expression of HMGB1 and HMGN2 in periodontistis.

The expression of HMGB1 and HMGN2 mRNA in gingival tissues and gingival crevicular fluid (GCF) in chronic periodontitis (CP), generalized aggressive periodontitis (G-AgP) patients and healthy subjects was detected by real-time PCR. The protein level of HMGB1 and HMGN2 in peri-implant crevicular fluid (PICF), peri-implant crevicular fluid of peri-implantitis (PI-PICF) and normal patients was determined by Western blotting. Furthermore, IL-1β, IL-6, IL-8, TNF-α and HMGB1 levels in GCF, PI-PICF and healthy -PICF samples from different groups were determined by ELISA.

HMGN2 expression was increased in inflamed gingival tissues and GCF from CP and G-ApG groups compared to control group. HMGB1 expression was the highest in the gingival tissues and GCF from CP patients and was accompanied by increased concentrations of IL-1β, IL-6, IL-8 proinflammaory cytokines. To our knowledge, this is the first study reporting that the expression of HMGB1 and HMGN2 was increased in the gingival tissues and GCF in CP and G-AgP and the PICF in PICF. Our data suggest that HMGB1 may be a potential target for the therapy of periodontitis and PI.

Antimicrobial peptides and periodontal disease

AIMS

The goal of this review is to identify the antimicrobial proteins in the oral fluids, saliva and gingival crevicular fluid and identify functional families and candidates for antibacterial treatment.

RESULTS

Periodontal biofilms initiate a cascade of inflammatory and immune processes that lead to the destruction of gingival tissues and ultimately alveolar bone loss and tooth loss. Treatment of periodontal disease with conventional antibiotics does not appear to be effective in the absence of mechanical debridement. An alternative treatment may be found in antimicrobial peptides and proteins, which can be bactericidal and anti-inflammatory and block the inflammatory effects of bacterial toxins. The peptides have co-evolved with oral bacteria, which have not developed significant peptide resistance. Over 45 antibacterial proteins are found in human saliva and gingival crevicular fluid. The proteins and peptides belong to several different functional families and offer broad protection from invading microbes. Several antimicrobial peptides and proteins (AMPs) serve as templates for the development of therapeutic peptides and peptide mimetics, although to date none have demonstrated efficacy in human trials.

CONCLUSIONS

Existing and newly identified AMPs may be developed for therapeutic use in periodontal disease or can serve as templates for peptide and peptide mimetics with improved therapeutic indices.

Expression of HMGB1 and HMGN2 in gingival tissues, GCF and PICF of periodontitis patients and peri-implantitis

BACKGROUND AND OBJECTIVE

High mobility group chromosomal protein B1 (HMGB1) and N2 (HMGN2), two members of high mobility group (HMG) family, play important role in inflammation. The purpose of this study was to investigate the expression of HMGB1 and HMGN2 in periodontistis.

MATERIALS AND METHODS

The expression of HMGB1 and HMGN2 mRNA in gingival tissues and gingival crevicular fluid (GCF) in chronic periodontitis (CP), generalised aggressive periodontitis (G-AgP) patients and healthy subjects was detected by real-time PCR. The protein level of HMGB1 and HMGN2 in peri-implant crevicular fluid (PICF), peri-implant crevicular fluid of peri-implantitis (PI-PICF) and normal patients was determined by Western blotting. Furthermore, IL-1β, IL-6, IL-8, TNF-α and HMGB1 levels in GCF, PI-PICF and healthy-PICF samples from different groups were determined by ELISA.

RESULTS

HMGN2 expression was increased in inflamed gingival tissues and GCF from CP and G-ApG groups compared to control group. HMGB1 expression was the highest in the gingival tissues and GCF from CP patients and was accompanied by increased concentrations of IL-1β, IL-6, IL-8 proinflammaory cytokines.

CONCLUSION

To our knowledge, this is the first study reporting that the expression of HMGB1 and HMGN2 was increased in the gingival tissues and GCF in CP and G-AgP and the PICF in PICF. Our data suggest that HMGB1 may be a potential target for the therapy of periodontitis and PI.

Psoriasin (S100A7) is a major Escherichia coli-cidal factor of the female genital tract

The female urogenital tract requires an efficient defense against bacteria, potentially derived from the adjacent intestinal tract. We have thus sought to identify the factors that protect against Escherichia coli (E. coli) in the female genital tract. Vaginal fluid from healthy human donors consistently killed E. coli in vitro and vaginal epithelium strongly expressed and secreted psoriasin. Psoriasin was constitutively produced in an organotypic vaginal epithelium model, and exposure of these cells to supernatants of E. coli cultures led to an enhanced psoriasin expression. Secreted psoriasin in vaginal fluids accounted for approximately 2.5-3% of total protein. Fractionation of vaginal fluids by high performance liquid chromatography (HPLC) showed that psoriasin co-eluted with a peak of E. coli killing activity. Our data show that normal vaginal fluid contains a powerful intrinsic antimicrobial defense against E. coli and that psoriasin contributes to the innate immune response of the female genital tract.

Identification and characterization of anti-microbial peptides from rabbit vaginal fluid

Antimicrobial peptides (AMPs) serve as a first line of host defense and represent an important, though poorly understood components of the innate immune system. The present study was an attempt to identify and characterize the major molecules having anti-bacterial activities from the vaginal fluid of rabbit, Oryctologus cuniculus. AMPs from the rabbit vaginal fluid (RVF) were identified in the acid extracts of pooled RVF samples after RP-HPLC purification. The protein, RVFAMP was effective against gram negative (Escherichia coli and Pseudomonas aeruginosa) and gram positive (Staphylococcus aureus and Streptococcus pyogenes) bacteria. The results of acid urea-PAGE-gel overlay assay (AU-PAGE-GOA) demonstrated clear zone of growth inhibition of E. coli corresponding to 6 and 15 kDa protein bands. LC-MS data of these proteins indicated that 15 kDa protein consists of lysozyme, lipopolysaccharide binding protein (LBP), hemoglobin-α and β subunits (Hb-α/β), whereas 9 kDa protein band consists of transthyretin and calcyclin while uteroglobulin and neutrophil antibacterial peptide-5 (NAMP-5) are present in the 6 kDa protein band. Of the eight proteins, Hb-α derived protein was further characterized, as it showed the highest Probability Based Mowse Score (PBMS) of 288. A 25mer peptide, RVFHbαp was active against several clinical pathogens as demonstrated by minimum inhibitory concentration (MIC) and radial diffusion assays (RDA). The interaction of RVFHbαP with bacterial liposome membrane was assessed by calcein dye leakage assay. RVFHbαP did not show cytotoxicity against human endocervical cells (End1/E6E7) or erythrocytes. RT-PCR and immunofluorescence results revealed the expression of RVFHbαP mRNA and protein in rabbit vaginal tissue. To the best our knowledge, this is the first report describing the detection of AMPs in RVFs. In conclusion, these studies indicated that vaginal epithelial cells (VEC) derived RVFHbαP may have therapeutic potential in the management of reproductive well being of rabbits. The major reason for undertaking this study in rabbits is that, it forms an excellent in vivo model system for human's studies.

The human male reproductive tract antimicrobial peptides of the HE2 family exhibit potent synergy with standard antibiotics

Reproductive tract infections pose a serious threat to health and fertility. Due to the emergence of antibiotic resistant pathogens, antimicrobial proteins and peptides of the reproductive tract are extensively characterized in recent years toward developing newer strategies to treat genital tract infections. Pathogen growth inhibition using a combination of naturally occurring male reproductive tract antimicrobial peptides and commonly used antibiotics has not been reported. Checker board analyses were carried out to determine the nature of interaction (synergistic, additive and antagonistic) between HE2alpha and HE2beta2 peptides and the commonly used antibiotics. Using Escherichia coli as the target organism, the minimal inhibitory concentration and fractional inhibitory concentration indices were determined. We demonstrate for the first time that the human male reproductive tract antimicrobial peptides HE2alpha and HE2beta2 act synergistically with the commonly used antibiotics to inhibit E. coli growth. A combination of HE2alpha and HE2beta2 peptides resulted in an additive effect. Interestingly, the synergistic effects of HE2 peptides were highest with doxycycline and ciprofloxacin, antibiotics generally used to treat epididymitis. Results of this study demonstrate the potential of endogenous HE2 peptides to be pharmacologically important in designing novel strategies to treat reproductive tract infections.

Rapid reprogramming of haemoglobin structure-function exposes multiple dual-antimicrobial potencies

The intrinsic cytotoxicity of cell-free haemoglobin (Hb) has hampered the development of reliable Hb-based blood substitutes for over seven decades. Notably, recent evidence shows that the Hb deploys this cytotoxic attack against invading microbes, albeit, through an unknown mechanism. Here, we unraveled a rapid molecular reprogramming of the Hb structure-function triggered by virulent haemolytic pathogens that feed on the haem-iron. On direct contact with the microbe, the Hb unveils its latent antimicrobial potency, where multiple antimicrobial fragments are released, each harbouring coordinated 'dual-action centres': microbe binding and pseudoperoxidase (POX) cycle activity. The activated Hb fragments anchor onto the microbe while the juxtaposed POX instantly unleashes a localized oxidative shock, killing the pathogen-in-proximity. This concurrent action conceivably restricts the diffusion of free radicals. Furthermore, the host astutely protects itself from self-cytotoxicity by simultaneously releasing endogenous antioxidants. We found that this decryption mechanism of antimicrobial potency is conserved in the ancient invertebrate respiratory protein, indicating its fundamental significance. Our definition of dual-antimicrobial centres in the Hb provides vital clues for designing a safer Hb-based oxygen carrier blood substitute.

Alpha and beta chains of hemoglobin inhibit production of Staphylococcus aureus exotoxins

Prior studies suggest Staphylococcus aureus exotoxins are not produced when the organism is cultured in human blood. Human blood was fractionated into plasma and water-lysed red blood cells, and it was demonstrated that mixtures of alpha and beta globins of hemoglobin (as low as 1 mug/mL) inhibited S. aureus exotoxin production while increasing production of protein A and not affecting bacterial growth. Pepsin but not trypsin digestion destroyed the ability of alpha and beta globin to inhibit exotoxin production. Exotoxin production by both methicillin-resistant and methicillin-susceptible organisms was inhibited. Production of streptococcal pyrogenic exotoxin A by Streptococcus pyogenes was unaffected by alpha and beta globin chains but was inhibited when produced in S. aureus. Use of isogenic S. aureus strains suggested the targets of alpha and beta globin chains, leading to inhibition of staphylococcal exotoxins, included the two-component system SrrA-SrrB. delta hemolysin production was also inhibited, suggesting the two-component (and quorum sensing) system AgrA-AgrC was targeted. The alpha and beta globin chains represent promising molecules to interfere with the pathogenesis of serious staphylococcal diseases.

Antimicrobial activity of histidine-rich peptides is dependent on acidic conditions

Synthetic peptides composed of multiples of the consensus heparin-binding Cardin and Weintraub sequences AKKARA and ARKKAAKA are antimicrobial. Replacement of lysine and arginine by histidine in these peptides completely abrogates their antimicrobial and heparin-binding activities at neutral pH. However, the antibacterial activity against Gram-negative (Escherichia coli, Pseudomonas aeruginosa) and Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) as well as the fungus Candida albicans, was restored at acidic conditions (pH 5.5). Fluorescence microscopy and FACS analysis showed that the binding of the histidine-rich peptides to E. coli and Candida was significantly enhanced at pH 5.5. Likewise, fluorescence studies for assessment of membrane permeation as well as electron microscopy analysis of peptide-treated bacteria, paired with studies of peptide effects on liposomes, demonstrated that the peptides induce membrane lysis only at acidic pH. No discernible hemolysis was noted for the histidine-rich peptides. Similar pH-dependent antimicrobial activities were demonstrated for peptides derived from histidine-rich and heparin-binding regions of human kininogen and histidine-rich glycoprotein. The results demonstrate that the presence of an acidic environment is an important regulator of the activity of histidine-rich antimicrobial peptides.