Purification, primary structure, and antimicrobial activities of a guinea pig neutrophil defensin

Structure-activity relationships of antibacterial peptides

Antimicrobial peptides play a crucial role in innate immunity, whose components are mainly peptide-based molecules with antibacterial properties. Indeed, the exploration of the immune system over the past 40 years has revealed a number of natural peptides playing a pivotal role in the defence mechanisms of vertebrates and invertebrates, including amphibians, insects, and mammalians. This review provides a discussion regarding the antibacterial mechanisms of peptide-based agents and their structure-activity relationships (SARs) with the aim of describing a topic that is not yet fully explored. Some growing evidence suggests that innate immunity should be strongly considered for the development of novel antibiotic peptide-based libraries. Also, due to the constantly rising concern of antibiotic resistance, the development of new antibiotic drugs is becoming a priority of global importance. Hence, the study and the understanding of defence phenomena occurring in the immune system may inspire the development of novel antibiotic compound libraries and set the stage to overcome drug-resistant pathogens. Here, we provide an overview of the importance of peptide-based antibacterial sources, focusing on accurately selected molecular structures, their SARs including recently introduced modifications, their latest biotechnology applications, and their potential against multi-drug resistant pathogens. Last, we provide cues to describe how antibacterial peptides show a better scope of action selectivity than several anti-infective agents, which are characterized by non-selective activities and non-targeted actions toward pathogens.

Modulation of ovine SBD-1 expression by Saccharomyces cerevisiae in ovine ruminal epithelial cells

Background

The ovine rumen is involved in host defense responses and acts as the immune interface with the environment. The ruminal mucosal epithelium plays an important role in innate immunity and secretes antimicrobial innate immune molecules that have bactericidal activity against a variety of pathogens. Defensins are cationic peptides that are produced by the mucosal epithelia and have broad-spectrum antimicrobial activity. Sheep β-defensin-1 (SBD-1) is one of the most important antibacterial peptides in the rumen. The expression of SBD-1 is regulated by the probiotic, Saccharomyces cerevisiae (S.c); however, the regulatory mechanism has not yet been elucidated. In the current study, the effects of S.c on the expression and secretion of SBD-1 in ovine ruminal epithelial cells were investigated using quantitative real-time PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). In addition, specific inhibitors were used to block the nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB), p38, JNK, and ERK1/2 signalling pathways separately or simultaneously, to determine the regulatory mechanism(s) governing S.c-induced SBD-1 upregulation.

Results

Incubation with S.c induced release of SBD-1 by ovine ruminal epithelial cells, with SBD-1 expression peaking after 12 h of incubation. The highest SBD-1 expression levels were achieved after treatment with 5.2 × 10⁷ CFU∙mL^− 1 S.c. Treatment with S.c resulted in significantly increased NF-κB, p38, JNK, ERK1/2, TLR2, and MyD88 mRNA expression. Whereas inhibition of mitogen-activated protein kinases (MAPKs) and NF-κB gene expression led to a decrease in SBD-1 expression.

Conclusions

S.c was induced SBD-1 expression and the S.c-induced up-regulation of SBD-1 expression may be related to TLR2 and MyD88 in ovine ruminal epithelial cells. This is likely simultaneously regulated by the MAPKs and NF-κB pathways with the p38 axis of the MAPKs pathway acting as the primary regulator. Thus, the pathways regulating S.c-induced SBD-1 expression may be related to TLR2-MyD88-NF-κB/MAPKs, with the TLR2-MyD88-p38 component of the TLR2-MyD88-MAPKs signalling acting as the main pathway.

Phage-Phagocyte Interactions and Their Implications for Phage Application as Therapeutics

Phagocytes are the main component of innate immunity. They remove pathogens and particles from organisms using their bactericidal tools in the form of both reactive oxygen species and degrading enzymes-contained in granules-that are potentially toxic proteins. Therefore, it is important to investigate the possible interactions between phages and immune cells and avoid any phage side effects on them. Recent progress in knowledge concerning the influence of phages on phagocytes is also important as such interactions may shape the immune response. In this review we have summarized the current knowledge on phage interactions with phagocytes described so far and their potential implications for phage therapy. The data suggesting that phage do not downregulate important phagocyte functions are especially relevant for the concept of phage therapy.

Differential Expression of Human Beta Defensin 2 and Human Beta Defensin 3 in Human Middle Ear Cholesteatoma

Objectives:

The purpose of this study was to investigate the differential expressions of human beta defensin ( hBD) 2 and hBD-3 in human middle ear cholesteatoma epithelium.

Methods:

The expressions of hBD-2 and hBD-3 were analyzed by quantitative real-time reverse transcription-poly-merase chain reaction (RT-PCR), Western blotting, and immunohistochemical staining. Samples were obtained from 10 patients who underwent middle ear surgery for middle ear cholesteatoma.

Results:

Real-time RT-PCR and Western blot analysis showed that the messenger RNAs and proteins of hBD-2 and hBD-3 were higher in the cholesteatoma epithelium than in normal external auditory canal skin. In cholesteatoma epithelium, hBD-2 and hBD-3 activities were present in the upper granular layer and in the prickle cell layer, but in the normal skin they were poorly expressed in all layers.

Conclusions:

Increased expressions of hBD-2 and hBD-3 in cholesteatoma epithelium suggest that cholesteatoma, a chronic inflammatory state of middle ear keratinocytes, may induce an innate immune response. That the induction of hBD-2 was found to be more intense than that of hBD-3 in cholesteatoma epithelium implies that hBD-2 is the major effector in terms of chronic epithelial inflammatory responses.

Antimicrobial Peptides in Human Sepsis

Nearly 100 years ago, antimicrobial peptides (AMPs) were identified as an important part of innate immunity. They exist in species from bacteria to mammals and can be isolated in body fluids and on surfaces constitutively or induced by inflammation. Defensins have anti-bacterial effects against Gram-positive and Gram-negative bacteria as well as anti-viral and anti-yeast effects. Human neutrophil peptides (HNP) 1-3 and human beta-defensins (HBDs) 1-3 are some of the most important defensins in humans. Recent studies have demonstrated higher levels of HNP 1-3 and HBD-2 in sepsis. The bactericidal/permeability-increasing protein (BPI) attenuates local inflammatory response and decreases systemic toxicity of endotoxins. Moreover, BPI might reflect the severity of organ dysfunction in sepsis. Elevated plasma lactoferrin is detected in patients with organ failure. HNP 1-3, lactoferrin, BPI, and heparin-binding protein are increased in sepsis. Human lactoferrin peptide 1-11 (hLF 1-11) possesses antimicrobial activity and modulates inflammation. The recombinant form of lactoferrin [talactoferrin alpha (TLF)] has been shown to decrease mortality in critically ill patients. A phase II/III study with TLF in sepsis did not confirm this result. The growing number of multiresistant bacteria is an ongoing problem in sepsis therapy. Furthermore, antibiotics are known to promote the liberation of pro-inflammatory cell components and thus augment the severity of sepsis. Compared to antibiotics, AMPs kill bacteria but also neutralize pathogenic factors such as lipopolysaccharide. The obstacle to applying naturally occurring AMPs is their high nephro- and neurotoxicity. Therefore, the challenge is to develop peptides to treat septic patients effectively without causing harm. This overview focuses on natural and synthetic AMPs in human and experimental sepsis and their potential to provide significant improvements in the treatment of critically ill with severe infections.

Mass spectral analysis of urine proteomic profiles of dairy cows suffering from clinical ketosis

BACKGROUND

Ketosis is an important metabolic disorder in dairy cows during the transition period. The urine proteomics of ketosis has not been investigated using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS).

OBJECTIVE

The aim is to determine differences between urine proteomic profiles of healthy cows and those with clinical ketosis, and facilitate studies of the underlying physiological and biochemical mechanisms that lead to liver pathology in ketosis.

ANIMALS AND METHODS

We analyzed the urine samples of 20 cows with clinical ketosis (group 1) and 20 control cows (group 2) using SELDI-TOF-MS.

RESULTS

Thirty-nine peptide peaks differed between both groups. Polypeptides corresponding to 26 of these differential peptide peaks were identified using the SWISS-PROT protein database. We found that the peaks of 11 distinct polypeptides from the urine samples of the ketosis group were significantly reduced, compared with those of the control group as based on the Wilcoxon rank sum test. Among these were VGF (non-acronymic) protein, amyloid precursor protein, serum amyloid A (SAA), fibrinogen, C1INH, apolipoprotein C-III, cystatin C, transthyretin, hepcidin, human neutrophil peptides, and osteopontin.

CONCLUSION

These proteins may represent novel biomarkers of the metabolic changes that occur in dairy cows with ketosis. Our results will help to better understand the physiological changes and pathogenesis observed in cows with ketosis.

CLINICAL IMPORTANCE

The SELDI-TOF-MS can be used to understand the physiological and biochemical mechanisms of ketosis and identify biomarkers of the disease.

Two fundamentals of mammalian defense in fungal infections: endothermy and innate antifungal immunity

The environment of animals is inhabited by enormous fungal species, but only a few hundreds are pathogenic for mammals. Most of potentially pathogenic fungal species, excluding dermatophytes, seldom cause the disease in immunocompetent hosts. Data from literature indicate, that an immune system and endothermy are foundations for this mammalian relative resistance to fungal systemic infections. Stable and high temperature of the body restricts invasion and growth of potentially pathogenic fungi. Together with elevated metabolism it supports the effectiveness of mammalian immunity. The innate immunity is assigned to prevent the invasion of various microbes (including fungi) to the hosts' organism. It consists of cellular receptors and several humoral factors as the Antimicrobial Peptides. If the physical barriers fail in stopping the invader, it is recognized as "alien" by multiple Pattern Recognition Receptors (PRRs) like Toll Like Receptors (TLRs) expressed by cells of innate immunity and/or C-type lectins. At the same time innate inflammation begins and the complement cascade is activated. These mechanisms are able to stop and clear some fungal infections. During existing infection the adaptive immunity is induced. This review aims to show the role of mammalian endothermy and to point the most important elements of innate antifungal immunity.

Mechanisms and modifications of naturally occurring host defense peptides for anti-HIV microbicide development

Despite advances in the treatment of HIV infection, heterosexual transmission of HIV remains high, and vaccines to prevent HIV acquisition have been unfruitful. Vaginal microbicides, on the other hand, have demonstrated considerable potential for HIV prevention, and a variety of compounds have been screened for their activity and safety as anti-HIV microbicides. Among these are the naturally occurring host defense peptides, small peptides from diverse lineages with intrinsic antiviral activity. Naturally occurring host defense peptides with anti-HIV activity are promising candidates for vaginal microbicide development. Their structural variance and accompanying mechanistic diversity provide a wide range of inhibitors whose antiviral activity can be exerted at nearly every stage of the HIV lifecycle. Additionally, peptide modification has been explored as a method for improving the anti-HIV activity of host defense peptides. Structure- and sequence-based alterations have achieved varying success in improving the potency and specificity of anti-HIV peptides. Overall, peptides have been discovered or engineered to inhibit HIV with therapeutic indices of > 1000, encouraging their advancement toward clinical trials. Here we review the naturally occurring anti-HIV host defense peptides, demonstrating their breadth of mechanistic diversity, and exploring approaches to enhance and optimize their activity in order to expedite their development as safe and effective anti-HIV vaginal microbicides.

α-Defensins in human innate immunity

Defensins are small, multifunctional cationic peptides. They typically contain six conserved cysteines whose three intramolecular disulfides stabilize a largely β-sheet structure. This review of human α-defensins begins by describing their evolution, including their likely relationship to the Big Defensins of invertebrates, and their kinship to the β-defensin peptides of many if not all vertebrates, and the θ-defensins found in certain non-human primates. We provide a short history of the search for leukocyte-derived microbicidal molecules, emphasizing the roles played by luck (good), preconceived notions (mostly bad), and proper timing (essential). The antimicrobial, antiviral, antitoxic, and binding properties of human α-defensins are summarized. The structural features of α-defensins are described extensively and their functional contributions are assessed. The properties of HD6, an enigmatic Paneth cell α-defensin, are contrasted with those of the four myeloid α-defensins (HNP1-4) and of HD5, the other α-defensin of human Paneth cells. The review ends with a decalogue that may assist researchers or students interested in α-defensins and related aspects of neutrophil function.

Characterization of the novel antibacterial peptide Leucrocin from crocodile (Crocodylus siamensis) white blood cell extracts

Four novel antibacterial peptides, Leucrocin I-IV from Siamese crocodile white blood cell extracts were purified by reverse phase high performance liquid chromatography (RP-HPLC). Leucrocins exhibit strong antibacterial activity towards Staphylococcus epidermidis, Salmonella typhi and Vibrio cholerae. The peptides were 7-10 residues in length with different primary structure. The amino acid sequence of Leucrocin I is NGVQPKY with molecular mass around 806.99 Da and Leucrocin II is NAGSLLSGWG with molecular mass around 956.3 Da. Further, the interaction between peptides and bacterial membranes as part of their killing mechanism was studied by fluorescence and electron microscopy. The outer membrane and cytoplasmic membrane was the target of action of Leucrocins as assayed in model membrane by release of β-galactosidase due to the membrane permeabilization. Finally, the hemolytic effect was tested against human red blood cell. Leucrocin I, III and IV showed less toxicity against human red blood cells than Leucrocin II.

Inhibition of bactericidal activity is maintained in a mouse alpha-defensin precursor with proregion truncations

alpha-Defensin biosynthesis requires the proteolytic conversion of inactive precursors to microbicidal forms. In mouse Paneth cell pro-alpha-defensin proCrp4((20-92)), anionic amino acids positioned near the proregion N-terminus inhibit proCrp4 activity by an apparent charge neutralization mechanism. Because most pro-alpha-defensins contain proregions of highly conserved chain length, we tested whether decreasing the distance between the inhibitory acidic residues of the proregion and the alpha-defensin component of the precursor would alter proCrp4 inhibition. Accordingly, two proCrp4 deletion variants, (Delta44-53)-proCrp4 and (Delta44-58)-proCrp4, truncated in a manner corresponding to deletions between MMP-7 cleavage sites, were prepared and assayed for bactericidal peptide activity. Consistent with the properties of full-length proCrp4((20-92)), (Delta44-53)-proCrp4 and (Delta44-58)-proCrp4 were processed effectively by MMP-7, lacked bactericidal activity at high peptide levels over a 3h exposure period, and failed to induce permeabilization of live Escherichia coliin vitro. Thus, bringing the inhibitory proregion domain into greater proximity with the Crp4 component of the precursor did not alter the activity of this pro-alpha-defensin. Therefore, the conserved distance that separates inhibitory acidic proregion residues from the Crp4 peptide is not critical to maintaining proCrp4((20-92)) in an inactive state.

The repertoire of equine intestinal alpha-defensins

Background

Defensins represent an important class of antimicrobial peptides. These effector molecules of the innate immune system act as endogenous antibiotics to protect the organism against infections with pathogenic microorganisms. Mammalian defensins are classified into three distinct sub-families (α-, β- and θ-defensins) according to their specific intramolecular disulfide-bond pattern. The peptides exhibit an antimicrobial activity against a broad spectrum of microorganisms including bacteria and fungi. Alpha-Defensins are primarily synthesised in neutrophils and intestinal Paneth cells. They play a role in the pathogenesis of intestinal diseases and may regulate the flora of the intestinal tract. An equine intestinal α-defensin (DEFA1), the first characterised in the Laurasiatheria, shows a broad antimicrobial spectrum against human and equine pathogens. Here we report a first investigation of the repertoire of equine intestinal α-defensins. The equine genome was screened for putative α-defensin genes by using known α-defensin sequences as matrices. Based on the obtained sequence information, a set of oligonucleotides specific to the α-defensin gene-family was designed. The products generated by reverse-transcriptase PCR with cDNA from the small intestine as template were sub-cloned and numerous clones were sequenced.

Results

Thirty-eight equine intestinal α-defensin transcripts were determined. After translation it became evident that at least 20 of them may code for functional peptides. Ten transcripts lacked matching genomic sequences and for 14 α-defensin genes apparently present in the genome no appropriate transcript could be verified. In other cases the same genomic exons were found in different transcripts.

Conclusions

The large repertoire of equine α-defensins found in this study points to a particular importance of these peptides regarding animal health and protection from infectious diseases. Moreover, these findings make the horse an excellent species to study biological properties of α-defensins. Interestingly, the peptides were not found in other species of the Laurasiatheria to date. Comparison of the obtained transcripts with the genomic sequences in the current assembly of the horse (EquCab2.0) indicates that it is yet not complete and/or to some extent falsely assembled.

Factors that deregulate the protective immune response in tuberculosis

Tuberculosis (TB) is a chronic infectious disease which essentially affects the lungs and produces profound abnormalities on the immune system. Although most people infected by the tubercle bacillus (90%) do not develop the disease during their lifetime, when there are alterations in the immune system, such as co-infection with HIV, malnutrition, or diabetes, the risk of developing active disease increases considerably. Interestingly, during the course of active disease, even in the absence of immunosuppressive conditions, there is a profound and prolonged suppression of Mycobacterium tuberculosis-specific protective immune responses. Several immune factors can contribute to downregulate the protective immunity, permitting disease progression. In general, many of these factors are potent anti-inflammatory molecules that are probably overproduced with the intention to protect against tissue damage, but the consequence of this response is a decline in protective immunity facilitating bacilli growth and disease progression. Here the most significant participants in protective immunity are reviewed, in particular the factors that deregulate protective immunity in TB. Their manipulation as novel forms of immunotherapy are also briefly commented.

The conserved salt bridge in human alpha-defensin 5 is required for its precursor processing and proteolytic stability

Mammalian alpha-defensins, expressed primarily in leukocytes and epithelia, play important roles in innate and adaptive immune responses to microbial infection. Six invariant cysteine residues forming three indispensable disulfide bonds and one Gly residue required structurally for an atypical beta-bulge are totally conserved in the otherwise diverse sequences of all known mammalian alpha-defensins. In addition, a pair of oppositely charged residues (Arg/Glu), forming a salt bridge across a protruding loop in the molecule, is highly conserved. To investigate the structural and functional roles of the conserved Arg(6)-Glu(14) salt bridge in human alpha-defensin 5 (HD5), we chemically prepared HD5 and its precursor proHD5 as well as their corresponding salt bridge-destabilizing analogs E14Q-HD5 and E57Q-proHD5. The Glu-to-Gln mutation, whereas significantly reducing the oxidative folding efficiency of HD5, had no effect on the folding of proHD5. Bovine trypsin productively and correctly processed proHD5 in vitro but spontaneously degraded E57Q-proHD5. Significantly, HD5 was resistant to trypsin treatment, whereas E14Q-HD5 was highly susceptible. Further, degradation of E14Q-HD5 by trypsin was initiated by the cleavage of the Arg(13)-Gln(14) peptide bond in the loop region, a catastrophic proteolytic event resulting directly in quick digestion of the whole defensin molecule. The E14Q mutation did not alter the bactericidal activity of HD5 against Staphylococcus aureus but substantially enhanced the killing of Escherichia coli. By contrast, proHD5 and E57Q-proHD5 were largely inactive against both strains at the concentrations tested. Our results confirm that the primary function of the conserved salt bridge in HD5 is to ensure correct processing of proHD5 and subsequent stabilization of mature alpha-defensin in vivo.

Comparative antiviral and proviral factors in semen and vaccines for preventing viral dissemination from the male reproductive tract and semen

Many animal and human viruses are disseminated via semen, but there is little information on how to measure and stimulate protective antiviral immunity in the male reproductive tract and semen. This information is important since successful vaccination through the stimulation of protective immune responses could be a mechanism to prevent viral contamination of semen and subsequent wide spread viral dissemination. Even control of the infection by shortening the duration of viral shedding and lowering the viral load in semen would lessen the chances of viral dissemination through this route. This review will highlight the current knowledge of immunity in the male reproductive tract and summarize ‘antiviral’ as well as ‘proviral’ factors in semen such as cytokines, cells, antibodies, antimicrobial peptides, enzymes, hormones and growth factors. These factors must provide a fine balance between ‘immunosuppression’ in semen needed to protect sperm viability and ‘immunocompetency’ to prevent pathogen contamination. The review will also suggest continuing challenges to researchers for preventing viral dissemination via semen and propose a large animal model for continued research in this important area.

A novel horse alpha-defensin: gene transcription, recombinant expression and characterization of the structure and function

Defensins are a predominant class of antimicrobial peptides, which act as endogenous antibiotics. Defensins are classified into three distinct sub-families: theta-, beta-, and alpha-defensins. Synthesis of alpha-defensin has been confirmed only in primates and glires to date and is presumably unique for a few tissues, including neutrophils and Paneth cells of the small intestine. Antimicrobial activities of these peptides were shown against a wide variety of microbes including bacteria, fungi, viruses and protozoan parasites. In the present study, we report the characterization of the equine alpha-defensin DEFA (defensin alpha) 1. Transcription analysis revealed that the transcript of the gene is present in the small intestine only. An alignment with known alpha-defensins from primates and glires displayed a homology with Paneth-cell-specific alpha-defensins. DEFA1 was recombinantly expressed in Escherichia coli and subsequently analysed structurally by CD and molecular modelling. To examine the antimicrobial properties, a radial diffusion assay was performed with 12 different micro-organisms and the LD90 (lethal dose killing > or =90% of target organism) and MBC (minimal bactericidal concentration) values were examined. DEFA1 showed an antimicrobial activity against different Gram-positive and Gram-negative bacteria and against the yeast Candida albicans. Using viable bacteria in combination with a membrane-impermeable fluorescent dye, as well as depolarization of liposomes as a minimalistic system, it became evident that membrane permeabilization is at least an essential part of the peptide's mode of action.

Defensins: endogenous antibiotic peptides from human leukocytes

A variety of endogenous antimicrobial peptides equip mammals, amphibians, insects and plants to defend themselves against microbial pathogens. Defensins are small peptides of mammalian cells that contain 29-35 amino acid residues, including six invariant cysteines that form three intramolecular disulphide bonds. They are produced by the sequential proteolysis of precursors that contain approximately 95 amino acids and are synthesized by several types of cells, especially the bone marrow precursors of blood neutrophils. Defensins constitute 5-7% of the total protein in human neutrophils and are present in high concentration in the azurophil granules and phagocytic vacuoles. The production of defensins by human neutrophils amounts to approximately 10 mg/kg body weight per day. In certain mammalian species lung macrophages and specialized epithelial (Paneth) cells in the small intestine also produce defensins. Defensins are complexly folded, amphipathic, rich in antiparallel beta-sheet but devoid of alpha-helical domains. Their unusually broad antimicrobial spectrum encompasses Gram-positive and Gram-negative bacteria, many fungi, mycobacteria, spirochetes and several enveloped viruses. The antimicrobial properties of defensins result from their insertion into target cell membranes and the formation of voltage-sensitive channels. Given their abundance and broad spectrum of antimicrobial activity, defensins may contribute substantially to innate resistance to infection.

Study of the Interaction of Human Defensins with Cell Membrane Models: Relationships between Structure and Biological Activity

The HNP-1, HNP-2, and HNP-3 defensins are human antimicrobial peptides produced in response to microbial invasion. Their properties are distinct, with a more potent action for HNP-3. In this study, the relationship between their structural dissimilarities and their different microbial actions was evaluated by molecular dynamics simulation. Structural determinants related to their intra- and intermolecular interactions were defined for each HNP using a simplified membrane model consisting of a water/n-hexane interface. The hydrophobic portion of the HNPs promotes their diffusion to the interface with a concomitant, slight change in the structure induced by the intermolecular electrostatic interactions between the HPN molecules and the interface. As a consequence, different orientations are probably adopted by the HNPs at the interface, which may explain their different actions. The interaction of HNP-1 and HNP-2 with the surfaces was also studied using Langmuir monolayers as a biomimetic system. It was found that peptides adsorb rapidly at n-hexane/water interfaces as well as at phospholipid Langmuir monolayers but not at the air/liquid interface. This reveals that the presence of an organic phase is required for the exposure of the hydrophobic groups of the peptides. In addition, adsorption kinetics and surface pressure-area isotherms for Langmuir monolayers suggested that the lipid-peptide interaction is strongly influenced by the monolayer electrical charge and packing, depending also on the HPN structure. This study supports a model in which defensins, acting in a dimeric form, are able to disrupt membranes. The model also shows that the individual structures of the HNPs are responsible for their different actions on microbes.

Overexpression of alpha-defensin is associated with bladder cancer invasiveness

Alpha-defensin (alpha-defensin) has been identified as a potential marker for bladder cancer in urine by surface enhanced laser desorption ionization studies, and confirmed using both immunoabsorption and immunodepletion studies. The objective of this study was to investigate the role of alpha-defensin in bladder cancer. Immunohistochemical analysis of tissue sections showed that alpha-defensin peptides are frequently expressed in bladder cancer cells. It is noteworthy that expression of alpha-defensins increased with tumor invasiveness. Surface enhanced laser desorption ionization analysis showed the presence of alpha-defensin in the T24 and A498 cancer cell lines. These cell lines show higher classically aggressive in vitro characteristics compared with the J82 cells that did not express alpha-defensin. Exogenously added alpha-defensin increased the proliferation and motility/invasiveness of these cell lines using respective assays. It is interesting that alpha-defensin peptides increased intracellular calcium ions (Ca2+). These data are consistent with a role for alpha-defensin in bladder cancer via modulation of cell motility and invasiveness using common intracellular signals, such as Ca2+. We propose that autocrine tumor expression of alpha-defensins may play an important role in facilitating the invasive phenotype of bladder cancer in patients.

Why Is the Arg5-Glu13 Salt Bridge Conserved in Mammalian α-Defensins?

Mammalian alpha-defensins, expressed primarily in leukocytes and epithelia, kill a broad range of microbes, constituting one of the first lines of innate immune defense against infection. Nine amino acid residues, including six cysteines, one glycine, and a pair of oppositely charged residues Arg/Glu, are conserved in the otherwise diverse sequences of all known mammalian alpha-defensins. Structural analysis indicates that the two charged residues form a salt bridge, likely stabilizing a protruding loop in the molecule. To investigate the structural and functional roles of the conserved Arg5-Glu13 salt bridge in alpha-defensins, we chemically prepared human neutrophil alpha-defensin 2 (HNP2) and five HNP2 analogs, R5E/E13R, E13Q, E13R, R5T/E13Y, and R14A. In contrast to HNP2 and R14A-HNP2, none of the four salt bridge analogs was capable of folding into a native conformation in the context of isolated defensin domains. However, when covalently attached to the 45-residue pro-HNP2 propeptide, the salt bridge analogs of HNP2 in their pro-forms all folded productively, suggesting that the Arg5-Glu13 salt bridge is not required for correct pro-alpha-defensin folding. When assayed against both Escherichia coli and Staphylococcus aureus, the six alpha-defensins showed bactericidal activity that correlated with the number of net positive charges carried by individual molecules in the panel, irrespective of whether or not the Arg5-Glu13 salt bridge was decimated, suggesting that Arg5 and Glu13 are not functionally conserved. Proteolytic resistance analysis with human neutrophil elastase, one major protease contained in azurophils with HNPs, revealed that destabilization of the salt bridge dramatically accelerated defensin degradation by the enzyme. Thus, we propose that the Arg5-Glu13 salt bridge found in most mammalian alpha-defensins is conserved for defensin in vivo stability.

Characterization of chlamydial genital infection resulting from sexual transmission from male to female guinea pigs and determination of infectious dose

A major problem in the study of chlamydial genital infections in animal models has been the use of varied doses of chlamydiae for infection in different laboratories. It is clearly desirable to use a dose which approximates that of natural sexual infection, but that dose to date has not been determined because of the inability of researchers to quantify chlamydiae in semen. Fortunately, sexual transmission of chlamydiae has been described for the guinea pig model of infection with the chlamydial agent of guinea pig inclusion conjunctivitis (GPIC). In this study, we undertook to determine the approximate infection dose in actual sexual transmission by comparing the kinetics of infection in female guinea pigs acquired via sexual contact to those of genital infections induced artificially with known quantities of chlamydiae. Groups of guinea pigs were infected intravaginally with 10(4), 10(3), 10(2), and 10(1) inclusion-forming units (IFU) of GPIC, and the kinetics of the infection were determined. Infection with 10(2) IFU produced infections with lower peak levels than those in animals receiving 10(4) or 10(3) IFU. Seventy percent of animals receiving 10(2) IFU became infected, while 100 and 79% of animals receiving 10(4) and 10(3) IFU, respectively, became infected. Animals receiving 10(2) IFU also had a longer incubation period. Of 19 animals that mated with infected males, 63.2% became infected, with an infection course which was not significantly different than that of the 10(2)-IFU-infected group. The data suggest that female guinea pigs received approximately 10(2) IFU by sexual transmission. Of interest was the observation that the guinea pigs infected by sexual transmission shed organisms for a significantly shorter time period than that of any group that was artificially infected. This result suggests that there may be factors associated with semen which passively transfer antimicrobial activity to the female or enhance the innate host response in the female. Immunization of females with an inactivated vaccine was also found to elicit a protective immune response against sexual challenge, demonstrating that the model can be used in the evaluation of possible vaccine candidates and/or methodologies. There is currently no other animal model available for any sexually transmitted disease in which the disease or the ability to prevent the disease may be studied in animals infected by the natural means.

Quantitative interactions between cryptdin-4 amino terminal variants and membranes

Paneth cells secrete alpha-defensins into the lumen from the base of small intestinal crypts, and cryptdin-4 (Crp4) is the most potent mouse alpha-defensin in vitro. Purified recombinant Crp4 and Crp4 variants with (des-Gly)-, (Gly1Val)-, (Gly1Asp)-, and (Gly1Arg)-substitutions were all bactericidal with Crp4 and (Gly1Arg)-Crp4 being slightly more active than other variants. Bactericidal activities correlated directly with permeabilization of live Escherichia coli, with equilibrium binding to E. coli membrane phospholipid bilayers and vesicles, and with induced graded fluorophore leakage from phospholipid vesicles. The Crp4 peptide N-terminus affects bactericidal activity modestly, apparently by influencing peptide binding to phospholipid bilayers and subsequent permeabilization of target cell membranes.

A possible molecular mechanism for the interaction of defensin with the sensory neuron membrane

A local membrane potential clamping method was used to study the effects of defensin NP-1 on the membranes of rat spinal ganglion neurons. NP-1 led to decreases in the effective charge for the activation gating system. This process depended on the NP-1 concentration. Use of the Hill equation showed that Kd was 2.10(-12) M and the Hill coefficient was 0.9. The structure of the defensin molecule was optimized using quantum chemical calculations based on a molecular mechanics method. The results obtained from these calculations suggested that a single hydroxyl group directed towards the outer part of thedefensin molecule and forming the carboxyl group of amino acid Glu14 could form a hydrogen bond with the active center of the membrane receptor. This explains the experimentally observed 1:1 stoichiometry of the ligand-receptor binding interaction between the defensin and the sensory neuron membrane.

The use of antimicrobial peptides in ophthalmology: an experimental study in corneal preservation and the management of bacterial keratitis

PURPOSE

Bacterial keratitis is an ocular infection with the potential to cause significant visual impairment. Increasing patterns of antibiotic resistance have necessitated the development of new antimicrobial agents for use in bacterial keratitis and other serious ocular infections. With a view to exploring the use of novel antimicrobial peptides in the management of ocular infection, we performed a series of experiments using synthetic antimicrobial peptides designed for the eradication of common and serious ophthalmic pathogens.

METHODS

Experiments were performed with three clinical ocular isolates--Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis--in three experimental settings: (1) in vitro in a controlled system of 10 mM sodium phosphate buffer, (2) in vitro in modified chondroitin sulfate-based corneal preservation media (Optisol), and (3) in an in vivo animal model (rabbit) simulating bacterial keratitis. In all cases, outcomes were measured by quantitative microbiological techniques.

RESULTS

The candidate peptides (CCI A, B, and C and COL-1) produced a total reduction of the test pathogens in phosphate buffered saline. In modified Optisol, the peptides were effective against S epidermidis at all temperatures, demonstrated augmented activity at 23 degrees C against the gram-positive organisms, but were ineffective against P aeruginosa. The addition of EDTA to the medium augmented the killing of P aeruginosa but made no difference in the reduction of gram-positive organisms. In an in vivo rabbit model of Pseudomonas keratitis, COL-1 demonstrated neither clinical nor microbicidal efficacy and appeared to have a very narrow dosage range, outside of which it appeared to be toxic to the ocular surface.

CONCLUSION

Our data indicate that the antimicrobial peptides we tested were effective in vitro but not in vivo. In an age of increasing antibiotic resistance, antimicrobial peptides, developed over millions of years as innate defense mechanisms by plants and animals, may have significant potential for development as topical agents for the management of severe bacterial keratitis. However, modifications of the peptides, the drug delivery systems, or both, will be necessary for effective clinical application.

Immunohistochemical study on expression of alpha-defensin and beta-defensin-2 in human buccal epithelia with candidiasis

OBJECTIVES AND DESIGN

It has been previously reported that alpha-defensin (HNPs) and beta-defensin-2 (HBD-2) peptides with antifungal and cytotoxic activities can be detected in oral carcinomas and the saliva of patients with oral carcinomas. The present study investigated the presence of HNPs and HBD-2 in oral epithelia with candidiasis.

MATERIALS AND METHODS

Tissue sections (4 microm) were prepared from biopsy and surgically removed specimens diagnosed as oral candidiasis (n = 10). The sections were examined immunohistochemically with antibodies directed against HNPs and HBD-2.

RESULTS

Tissue sections of oral candidiasis were immunostained with antidefensin antibodies. Neutrophils in the inflamed lamina propria were positively immunostained with anti-HNPs antibody. The cytoplasm of cells in the upper spinous layer, in the lower spinous layer and in the parakeratinized layer of buccal epithelia with candidiasis was immunostained intensely with anti-HBD-2 antibody. In contrast, the expression of HBD-2 in the normal spinous layer was much weaker than that in oral candidiasis. No signals of HNPs were found in normal buccal epithelium.

CONCLUSION

Buccal specimens from individuals with oral candidiasis show greater levels of expression of both HNPs and HBD-2. There might be a dual protection manner by defensins against fungal inflammation in infected buccal epithelia locally. Generally, HBD-2 signals have been found everywhere in the buccal epithelium; however, in an infected area, the signal intensity of HBD-2 has increased. HNPs signals have not been found in the normal buccal epithelium; however, HNPs signals have increased when the infection occurred.

Characterization of luminal paneth cell alpha-defensins in mouse small intestine. Attenuated antimicrobial activities of peptides with truncated amino termini

Paneth cells at the base of small intestinal crypts secrete apical granules that contain antimicrobial peptides including alpha-defensins, termed cryptdins. Using an antibody specific for mouse cryptdin-1, -2, -3, and -6, immunogold-localization studies demonstrated that cryptdins are constituents of mouse Paneth cell secretory granules. Several cryptdin peptides have been purified from rinses of adult mouse small intestine by gel filtration and reverse-phase high performance liquid chromatography. Their primary structures were determined by peptide sequencing, and their antimicrobial activities were compared with those of the corresponding tissue forms. The isolated luminal cryptdins included peptides identical to the tissue forms of cryptdin-2, -4, and -6 as well as variants of cryptdin-1, -4, and -6 that have N termini truncated by one or two residues. In assays of antimicrobial activity against Staphylococcus aureus, Escherichia coli, and the defensin-sensitive Salmonella typhimurium phoP(-) mutant, full-length cryptdins had the same in vitro antibacterial activities whether isolated from tissue or from the lumen. In contrast, the N-terminal-truncated (des-Leu), (des-Leu-Arg)-cryptdin-6, and (des-Gly)-cryptdin-4 peptides were markedly less active. The microbicidal activities of recombinant cryptdin-4 and (des-Gly)-cryptdin-4 peptides against E. coli, and S. typhimurium showed that the N-terminal Gly residue or the length of the cryptdin-4 N terminus are determinants of microbicidal activity. Innate immunity in the crypt lumen may be modulated by aminopeptidase modification of alpha-defensins after peptide secretion.

Effect of lysozyme or modified lysozyme fragments on DNA and RNA synthesis and membrane permeability of Escherichia coli

Previously we have shown that chicken egg white lysozyme, an efficient bactericidal agent, affects both gram-positive and gram-negative bacteria independently of its muramidase activity. More recently we reported that the digestion of lysozyme by clostripain yielded a pentadecapeptide, IVSDGNGMNAWVAWR (amino acid 98-112 of chicken egg white lysozyme), with moderate bactericidal activity but without muramidase activity. On the basis of this amino acid sequence three polypeptides, in which asparagine 106 was replaced by arginine (IVSDGNGMRAWVAWR, RAWVAWR, RWVAWR), were synthesized which showed to be strongly bactericidal. To elucidate the mechanisms of action of lysozyme and of the modified antimicrobial polypeptides Escherichia coli strain ML-35p was used. It is an ideal organism to study the outer and the inner membrane permeabilization since it is cryptic for periplasmic beta-lactamase and cytoplasmic beta-galactosidase unless the outer or inner membrane becomes damaged. For the first time we present evidence that lysozyme inhibits DNA and RNA synthesis and in contrast to the present view is able to damage the outer membrane of Escherichia coli. Blockage of macromolecular synthesis, outer membrane damage and inner membrane permeabilization bring about bacterial death. Ultrastructural studies indicate that lysozyme does not affect bacterial morphology but impairs stability of the organism. The bactericidal polypeptides derived from lysozyme block at first the synthesis of DNA and RNA which is followed by an increase of the outer membrane permeabilization causing the bacterial death. Inner membrane permeabilization, caused by RAWVAWR and RWVAWR, follows after the blockage of macromolecular synthesis and outer membrane damage, indicating that inner membrane permeabilization is not the deadly event. Escherichia coli bacteria killed by the substituted bactericidal polypeptides appeared, by electron microscopy, with a condensed cytoplasm and undulated bacterial membrane. So the action of lysozyme and its derived peptides is not identical.

Isolation, characterization, cDNA cloning, and antimicrobial properties of two distinct subfamilies of alpha-defensins from rhesus macaque leukocytes

Experiments to isolate and characterize rhesus macaque myeloid alpha-defensins (RMADs) were conducted. Seven RMAD peptides were isolated and sequenced, and the cDNAs encoding six of these peptides and one other alpha-defensin from bone marrow were also characterized. Four of the RMADs were found to be highly similar to human neutrophil alpha-defensins HNP-1 to HNP-3, while the remaining four peptides were much more similar to human enteric alpha-defensin HD-5. Two alpha-defensin pairs differed only by the presence or absence of an additional arginine at the amino termini of their mature peptides, indicative of alternate posttranslational processing. The primary translation products of RMAD-1 to -8 are 94- and 96-amino-acid prepropeptides that are highly similar to those of human alpha-defensins. Immunolocalization experiments revealed a granular cytoplasmic pattern in the cytoplasms of neutrophils, indistinguishable from the pattern observed after immunostaining of human myeloid alpha-defensins in polymorphonuclear leukocytes. Each of the purified peptides was tested for its in vitro activities against Staphylococcus aureus 502a, Listeria monocytogenes EGD, Escherichia coli ML35, and Cryptococcus neoformans 271A. Several of the peptides were microbicidal for the gram-positive bacteria and C. neoformans at defensin concentrations in the range of 2 to 5 microM. All of the peptides were bacteriostatic against E. coli, but none were bactericidal for this organism. This study is the first to characterize the sequences and activities of alpha-defensins from nonhuman primates, data that should aid in delineating the role of these peptides in rhesus macaque host defense.

Isolation and characterization of a novel antifungal peptide from Aspergillus niger

A novel antifungal peptide (termed as Anafp) was isolated from the culture supernatant of the filamentous fungi, Aspergillus niger. The whole amino acid sequence of Anafp was determined and the peptide was found to be composed of a single polypeptide chain with 58 amino acids including six cysteine residues. The peptide shows some degree of sequence homology to a cysteine-rich antifungal peptides reported from the seeds of Sinapis alba and Arabidopsis thaliana or the extracellular media of Aspergillus giganteus and Penicillium chrysogenumsome. Cysteine-spacing pattern of Anafp was similar to that of the antifungal peptide from Penicillium chrysogenum. The Anafp exhibited potent growth inhibitory activities against yeast strains as well as filamentous fungi at a range from 4 to 15 microM. In contrast, Anafp did not show antibacterial activity against Escherichia coli and Bacillus subtilis even at 50 microM.

Cecropin D-like antibacterial peptides from the sphingid moth, Agrius convolvuli

Two major antibacterial peptides were isolated and purified from immunized larval hemolymph of Agrius convolvuli. Acid extraction, gel filtration, ultrafiltration, and reversed-phase FPLC were used for purification of peptides. These peptides had similar molecular mass and amino acid composition. Moreover, 21 of the first 23 N terminal residues were identical. The peptides were highly homologous with cecropin D in size and primary sequence, and named Agrius cecropin D1 and D2. The molecular masses of Agrius cecropin D1 and D2 were 3,879.39 and 3,839.27, respectively. In antibacterial and hemolytic assays, Agrius cecropin D showed potent antibacterial activities against a panel of Gram positive and negative bacteria without hemolytic activity against human red blood cells. Notably, our antibacterial assay revealed Agrius cecropin D possessed stronger or at least equivalent activities against B. megaterium than cecropin A. It suggests that Agrius cecropin D, which has an alternative structure from cecropin D, could be the model for the development of peptide antibiotics. Arch.

Beta-sheet antibiotic peptides as potential dental therapeutics

Small, cysteine-rich, beta-sheet peptide antibiotics are found throughout the Animalia. Though broad spectrum in potential, they may exert selective antimicrobial effects under certain conditions. We have explored the antimicrobial properties of two families of beta-sheet peptide antibiotics, defensins and protegrins, against periodontopathic bacteria. The rabbit defensin NP-1 was active against facultative Gram-negative bacteria associated with early onset periodontitis, including Actinobacillus actinomycetemcomitans and the Capnocytophaga spp. Porcine protegrins showed even greater activity against those organisms, as well as against anaerobic bacteria associated with adult periodontitis, including Porphyromonas gingivalis Prevotella intermedia and Fusobacterium nucleatum. Based on these observations, we believe that protegrin-like beta-sheet peptide antibiotics may be useful dental therapeutics.

Semidry electroblotting of peptides and proteins from acid-urea polyacrylamide gels

A semidry electrophoretic transfer method was developed for efficient electroblotting of proteins separated by acid-urea polyacrylamide gel electrophoresis (AU-PAGE). Model polypeptides ranging from 1.8 to 21.5 kDa were used to test transfer parameters that included time of transfer, power settings, transfer solutions, and membrane type. Optimized conditions were identified which allowed for transfer efficiencies of 70-100% following 5-15 min of applied current. The best transfer solution was 5% acetic acid, the same solvent used for electrophoresis. Therefore, acid-urea gels could be subjected to electrophoretic transfer without a soaking step, thereby reducing loss of band resolution and eliminating leaching of protein from the gel. The method was shown to be applicable to Western blot analysis of rat neutrophil defensins.

Purification and in vitro activities of rabbit platelet microbicidal proteins

Recent in vitro studies have demonstrated that rabbit platelets release a small, cationic antimicrobial protein in response to thrombin stimulation under physiological conditions (M. R. Yeaman, S. M. Puentes, D. C. Norman, and A. S. Bayer, Infect. Immun. 60:1202-1209, 1992). This observation prompted our present investigation, focused on determining the array of antimicrobial proteins contained within rabbit platelets and their in vitro activity against common bloodstream pathogens. A group of small (6.0- to 9.0-kDa), cationic proteins with in vitro antimicrobial activity was purified from whole and thrombin-stimulated rabbit platelets by gel filtration and reversed-phase high-performance liquid chromatography. Purified proteins in micromolar concentrations (10 to 40 microg/ml) exerted in vitro microbiostatic and/or microbicidal activities against Staphylococcus aureus, Escherichia coli, and Candida albicans in a dose-dependent manner. The antimicrobial activities of proteins purified from rabbit platelet acid extracts were generally inversely related to pH, with maximal activity observed at pH 5.5. In contrast, the predominant protein isolated from thrombin-stimulated rabbit platelets, though biochemically and microbiologically similar to proteins extracted by acid, exhibited antimicrobial activities which were modestly enhanced at pH 7.2 compared with pH 5.5. Amino acid compositional analyses in combination with molecular mass determinations suggest that the majority of these proteins are distinct molecules not derived from a single common precursor. Collectively, these data indicate that rabbit platelets contain proteins which exert potent in vitro antimicrobial activity against bacterial and fungal pathogens which commonly invade the bloodstream. Moreover, several of these proteins were released from platelets stimulated with thrombin under physiological conditions and exerted potent antimicrobial activities in physiological pH ranges. These observations support the hypothesis that platelets serve an important role in host defense against infection, via localized release of antimicrobial proteins in response to stimuli associated with tissue injury or microbial colonization.

Intramolecular disulfide bonds enhance the antimicrobial and lytic activities of protegrins at physiological sodium chloride concentrations

Protegrins are 2-kDa antimicrobial peptides that contain 16-18 amino acid residues and two intramolecular disulfide bonds. We studied the contribution of these disulfide bonds to the bactericidal activity of protegrins in physiological concentrations of NaCl by comparing protegrin PG-1 with variants that lacked one or both cysteine disulfides. Whereas the bactericidal and liposome-lytic properties of protegrin PG-1 were enhanced by adding 100 mM NaCl to the phosphate-buffered medium, NaCl addition strongly inhibited the effects of its linearized, disulfide-free variant, [A6, A8, A13, A15]protegrin-1. Whereas protegrin PG-1 manifested beta-sheet structure by CD (circular dichroism) and ATR-FTIR (attenuated-total-reflectance-Fourier-transform-infrared) spectroscopy in buffer or membrane-mimetic environments, [A6, A8, A13, A15]protegrin-1 manifested disordered structure in phosphate buffer and alpha-helical characteristics in membrane-mimetic environments. Both single-disulfide protegrin variants, [A8, A13]protegrin-1 and [A6, A15]protegrin-1, assumed beta-sheet conformations with liposomes that simulated bacterial membranes, and both retained substantial bactericidal activity when 100 mM NaCl was present. These findings demonstrate that the intramolecular disulfide bonds of protegrins are required for their antiparallel beta-sheet conformation in membrane-mimetic environments and for their potent antimicrobial activity in media containing NaCl concentrations comparable to those found in serum and extracellular fluids.

Isolation of a peptide structurally related to mammalian corticostatins from the lamprey Petromyzon marinus

Peptides in an extract of skin from the agnathan Petromyzon marinus (sea lamprey) were purified by reversed-phase high-performance liquid chromatography and characterized by Edman degradation. The primary structure of a cysteine- and arginine-rich peptide (termed lamprey corticostatin-related peptide [LCRP]) was established as Cys-Pro-Cys-Gly-Arg-Arg-Arg-Cys-Cys-Val-Arg-Gly-Leu-Asn-Val-Tyr-Cys-Cys- Phe. Mass spectrometry indicated that all cysteine residues are intramolecularly linked. This amino acid sequence shows structural similarity to rat corticostatin R4 and rabbit corticostatin R1. In particular, LCRP contains the polyarginine sequence at the N-terminus of the peptide that is believed to mediate both the inhibition of ACTH stimulated steroidogenesis and the antimicrobial (defensin-like) actions of the corricostatins.

In vitro activity of the antimicrobial peptides human and rabbit defensins and porcine leukocyte protegrin against Mycobacterium tuberculosis

Three independent assay methods were used to investigate the activities of antimicrobial peptides (human and rabbit defensins and protegrin from porcine leukocytes) against Mycobacterium tuberculosis in vitro. M. tuberculosis H37Ra was cultured in the presence of human neutrophil peptide 1, synthetic rabbit neutrophil peptide 1, or porcine protegrin 1 at 37 degrees C for 6 to 48 h, and antimycobacterial activity was measured by CFU assay. These peptides at a concentration of 50 microg/ml showed significant antibacterial effects on M. tuberculosis after 24 and 48 h of incubation (85.9 to 97.5% at 24 h and 91.6 to 99.4% at 48 h). A radiometric method and a radial diffusion assay confirmed these observations. Antibacterial activity against M. tuberculosis was independent of calcium (1.0 mM) or magnesium (1.0 mM) and not inhibited by sodium chloride (100 mM). The optimal pH for antibacterial activity against M. tuberculosis was greater than 4.0. Three clinical isolates of M. tuberculosis were also studied, and these peptides showed 86.3 to 99.0% reduction in CFU of these organisms. Morphological studies using scanning electron microscopy showed that defensins caused lesions on the surface of H37Ra. These observations suggest that antimicrobial peptides such as defensins and protegrins may represent an important component of the host defense mechanism against M. tuberculosis and offer a potential new approach to therapy.

Isolation of an ovine pulmonary surfactant-associated anionic peptide bactericidal for Pasteurella haemolytica

Ovine pulmonary surfactant is bactericidal for Pasteurella haemolytica when surfactant and bacteria mixtures are incubated with normal ovine serum. To isolate this component, surfactant (1 mg/ml) was centrifuged at 100,000 x gav, and the supernatant was fractionated by HPLC. Fractions were eluted with acetonitrile (10-100%)/0.1% trifluoracetic acid and tested for bactericidal activity. Amino acid and sequence analysis of three bactericidal fractions showed that fraction 2 contained H-GDDDDDD-OH, fraction 3 contained H-DDDDDDD-OH, and fraction 6 contained H-GADDDDD-OH. Peptides in 0.14 M NaCl/10 microM ZnCl2 (zinc saline solution) induced killing of P. haemolytica and other bacteria comparable to defensins and beta-defensins [minimal bactericidal concentration (MBC)50 range, 0.01-0.06 mM] but not in 0.14 M NaCl/10 mM sodium phosphate buffer, pH 7.2/0.5 mM CaCl2/0.15 mM MgCl2 (MBC50 range, 2.8-11.5 mM). Bactericidal activity resided in the core aspartate hexapeptide homopolymeric region, and MBC50 values of aspartate dipeptide-to-heptapeptide homopolymers were inversely proportional to the number of aspartate residues in the peptide. P. haemolytica incubated with H-DDDDDD-OH in zinc saline solution was killed within 30 min. Ultrastructurally, cells contained flocculated intracellular constituents. In contrast to cationic defensins and beta-defensins, surfactant-associated anionic peptides are smaller in size, opposite in charge, and are bactericidal in zinc saline solution. They are members of another class of peptide antibiotics containing aspartate, which when present in pulmonary secretions may help clear bacteria as a part of the innate pulmonary defense system.

Inheritance of unequal numbers of the genes encoding the human neutrophil defensins HP-1 and HP-3

It is unclear whether the six known human defensin peptides are all encoded by separate genes or whether some of them are allelic. Three of the peptides, HP-1, HP-2, and HP-3, differ by only one amino acid, and it is thought that HP-2 may represent a proteolytic product of HP-1 and/or HP-3. To help determine the relationship of these three proteins, we isolated a nearly full-length cDNA encoding HP-1 with a sequence very similar to, but different from, the previously isolated HP-1 and -3 cDNAs. Gene copy number experiments established that there were at least two but fewer than five defensin genes with a high level of similarity to the HP-1 cDNA (HP-1/3-like). Three genomic clones were isolated that contained two different configurations of the HP-1/3-like sequences. Sequencing established that one encoded the HP-1 peptide, whereas the other encoded HP-3. Analysis of DNAs obtained from 18 unrelated individuals by Southern blot analysis revealed the expected fragments as well as additional fragments that were not present in the genomic clones. This suggested the possibility of alleles; however, when DNAs from families were examined, these fragments did not segregate in an obvious Mendelian fashion. The HP-1/3-like defensin genes are on human chromosome 8. Surprisingly, somatic cell hybrid mapping showed that the number of HP-1/3-like genes on isolated copies of chromosome 8 was variable. We conclude that individuals can inherit versions of chromosome 8 harboring either two or three copies of the genes that encode the HP-1, HP-2, and/or HP-3 peptides.

A novel antibacterial peptide family isolated from the silkworm, Bombyx mori

Three structurally related and novel antibacterial peptides have been isolated from the haemolymph of the silkworm, Bombyx mori, immunized with Escherichia coli. These peptides were 32 amino acids long and characteristically rich in proline residues. A unique threonine residue in each peptide was O-glycosylated and the modification seemed to be important for expression of antibacterial activity. The primary structure and antibacterial character of the novel peptides resemble those of abaecin (41% identity in amino acid sequence), an antibacterial peptide of the honeybee, although abaecin is not O-glycosylated. Incubation of the novel peptides with a liposome preparation caused leakage of entrapped glucose under low-ionic-strength conditions, suggesting that a target of the peptides is the bacterial membrane. We propose the name 'lebocin' for the novel peptide family isolated from B. mori.

Morphology of defensin-treated Staphylococcus aureus

Defensins are a family of broad-spectrum antimicrobial peptides found abundantly in the cytoplasmic granules of mammalian neutrophils and Paneth cells of the small intestine. Defensins are known to form ion channels on the membranes of target cells. These channel formations and the cytotoxicity of defensins are intimately linked. We showed the morphological effects of defensins on the cytoplasmic membranes of Staphylococcus aureus by transmission electron microscopy. S. aureus exposed to defensins developed characteristic mesosome-like structures but did not show remarkable changes in cell walls. Defensins induced such structural changes not only at high concentration but also at low concentrations that were not bactericidal. We also showed that increasing the concentration of NaCl in the reaction mixture completely inhibited the occurrence of membranous changes of target cells exposed to defensins. These findings are, to our knowledge, the first report of morphological changes in gram-positive bacteria treated with defensins. Our results indicate that the first effect of defensins in S. aureus is to damage cytoplasmic membranes directly; they also support previous reports that the cell membrane is the principal target of defensins.

Defensins

Defensins are a family of small cationic, antibiotic peptides that contain six cysteines in disulfide linkage. The peptides are abundant in phagocytes and small intestinal mucosa of humans and other mammals and in the hemolymph of insects. They contribute to host defense against microbes and may participate in tissue inflammation and endocrine regulation during infection. Bioengineered defensins are potentially useful as prophylactic and therapeutic agents in infections.

Effect of a chemical or proteolytic modification on the biological activity of guinea-pig cationic peptide

Guinea-pig neutrophil cationic peptides (GNCPs) are single polypeptides containing 31 amino acid residues and three intramolecular disulfide bonds, which show both antibacterial and histamine-releasing activities. Reduction and alkylation of the disulfide bonds of GNCP did not reduce both biological activities. When pyridylethylated GNCP was digested with trypsin, the biological activities were almost lost, whereas the chymotryptic digest retained the biological activities. Chymotrypsin digested fragments were purified by RP-HPLC, and three active peptide fragments containing two Arg residues at the N-terminal sequence were isolated. When the biological activities were examined using synthetic peptides containing various numbers of Arg residue at the N-terminus, the omission of the Arg residues was found to reduce remarkably the antibacterial and histamine-releasing activities. Together these observations indicate that the primary structures containing Arg residues at the N-terminus but not the intramolecular disulfide cross-linking are important for the expression of the biological activities of GNCP.

Antibacterial proteins from porcine polymorphonuclear neutrophils

Antibacterial peptides were purified from porcine neutrophil granules collected from healthy pigs. Granule proteins, extracted with 0.2 mol/L sodium acetate were subjected to ion-exchange chromatography and five peaks (designated A to E) were detected. Individual porcine neutrophil granule proteins were shown to inhibit the growth of target organisms Escherichia coli and Staphylococcus aureus. The antimicrobial activity was shown to be concentration and time dependent. Peak D showed strong antimicrobial activity against S. aureus and peak C (with a greater number of eluted proteins) was shown to be active against both S. aureus and E. coli. One of the peptides was purified further by reverse-phase HPLC from peak fraction C. The MW of this peptide was approximately 5500 Da as determined by SDS-PAGE and mass spectral analysis and was active against both E. coli and S. aureus in vitro sustaining a > 90% decrease, respectively, in CFU after a 2 h exposure with 50 micrograms of this peptide. Amino acid analysis showed the peptide was rich in aspartate/aspartic acid, glutamine/glutamic acid, proline, arginine and threonine. The antimicrobial activity of this peptide and other novel proteins in porcine neutrophilic granules demonstrates the probable role of these proteins and peptides in host defence of porcine neutrophils against bacterial infection.

In vitro activity of naturally occurring peptides (defensins) against Listeria monocytogenes

Autoclaved distilled water samples were inoculated with L. monocytogenes strain V7 and strain VPH-1, and incubated aerobically, at 30 C for 48 hours. Each strain was tested individually, and growth curves were determined at 1, 2, 3, 4, 5, 21, 24, and 48 hours. The growth or survival of L. monocytogenes was similar for both strains, with survivors at 24 hour-incubation. The microbicidal activity of one synthetic cationic peptide (NP-2) was examined against L. monocytogenes strain V7, in a water system. Antibacterial activity of NP-2 (1, 5, and 10 g/ml) was best expressed at 60 minute-incubation, with 10 g/ml of peptide, at 30 C.

Mouse Paneth cell defensins: primary structures and antibacterial activities of numerous cryptdin isoforms

Cryptdins are antimicrobial peptides of the defensin family that are produced by intestinal Paneth cells. mRNAs encoding 17 cryptdin isoforms have been characterized from a cDNA library generated from a single jejunal crypt. Six cryptdin cDNAs correspond to known peptides, and the remainder predict 11 novel Paneth cell defensins. Most cryptdin cDNAs have > or = 93% nucleotide sequence identity overall, except for cryptdin 4 and 5 cDNAs, whose respective mature peptide-encoding regions are only 74 and 78% identical to that of cryptdin 1. Cryptdin cDNAs differ at a small number of nucleotide positions: frequent substitutions were found in codons 38 and 52 of the propiece and in codons 68, 73, 76, 87, and 89 of the deduced peptides; cDNA clones with changes in codons 74, 83, and 88 were found, but there were fewer of these. The antimicrobial activities of cryptdins 1 to 6 were tested against Escherichia coli ML35 in two assays. In an agar diffusion assay, the potencies of cryptdins 1 to 3, 5, and 6 were approximately equivalent to that of rabbit neutrophil defensin NP-1 but cryptdin 4 was 30 times more active than NP-1. In a bactericidal assay system, cryptdins 1 and 3 to 6 were equally active at 10 micrograms/ml but cryptdin 2 and rabbit NP-1 were not active at this concentration. Since cryptdins 2 and 3 differ only at residue 10 (Thr and Lys, respectively), this amino acid appears to function in bactericidal interaction with E. coli. The demonstration that Paneth cells express a diverse population of microbicidal defensins further implicates cryptdins in restricting colonization or invasion of small intestinal epithelium by bacteria.