Studies of the biological properties of human beta-defensin 1

Incorporation of human β-defensin-1 into immunoliposomes to facilitate targeted autophagy therapy of colon carcinoma

Based on the discovery that human β-defensin-1 (hBD-1) triggers autophagy in colon cancer cells and inhibits proliferation, we proposed the consideration of its druggability. As a protein, its stability, targetability and bioavailability must be improved. Compared with the traditional medicinal chemistry technology, nanotechnology is more economical for increasing the druggability of hBD-1 and can be readily scaled up. Here, we propose an immunoliposome system containing hBD-1 to improve its stability and bioavailability. To enhance its targetability, anti-epidermal growth factor receptor (EGFR) antibodies were conjugated to the liposomal bilayer to produce immunoliposomes that can target EGFR, which is highly expressed in colon cancer cells. Although more studies are needed to support clinical trials and large-scale manufacturing, these immunoliposomes have great potential as therapeutics. Thus, immunoliposomes are suitable nanovesicles to improve the druggability of hBD-1; however, additional basic and translational research of these systems is warranted.

SARS-CoV-2, periodontal pathogens, and host factors: The trinity of oral post-acute sequelae of COVID-19

COVID-19 as a pan-epidemic is waning but there it is imperative to understand virus interaction with oral tissues and oral inflammatory diseases. We review periodontal disease (PD), a common inflammatory oral disease, as a driver of COVID-19 and oral post-acute-sequelae conditions (PASC). Oral PASC identifies with PD, loss of teeth, dysgeusia, xerostomia, sialolitis-sialolith, and mucositis. We contend that PD-associated oral microbial dysbiosis involving higher burden of periodontopathic bacteria provide an optimal microenvironment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. These pathogens interact with oral epithelial cells activate molecular or biochemical pathways that promote viral adherence, entry, and persistence in the oral cavity. A repertoire of diverse molecules identifies this relationship including lipids, carbohydrates and enzymes. The S protein of SARS-CoV-2 binds to the ACE2 receptor and is activated by protease activity of host furin or TRMPSS2 that cleave S protein subunits to promote viral entry. However, PD pathogens provide additional enzymatic assistance mimicking furin and augment SARS-CoV-2 adherence by inducing viral entry receptors ACE2/TRMPSS, which are poorly expressed on oral epithelial cells. We discuss the mechanisms involving periodontopathogens and host factors that facilitate SARS-CoV-2 infection and immune resistance resulting in incomplete clearance and risk for 'long-haul' oral health issues characterising PASC. Finally, we suggest potential diagnostic markers and treatment avenues to mitigate oral PASC.

Defensins: The natural peptide antibiotic

Defensins are a family of cationic antimicrobial peptides active against a broad range of infectious microbes including bacteria, viruses and fungi, playing important roles as innate effectors and immune modulators in immunological control of microbial infection. Their antibacterial properties and unique mechanisms of action have garnered considerable interest in developing defensins into a novel class of natural antibiotic peptides to fend off pathogenic infection by bacteria, particularly those resistant to conventional antibiotics. However, serious pharmacological and technical obstacles, some of which are unique to defensins and others are common to peptide drugs in general, have hindered the development and clinical translation of defensins as anti-infective therapeutics. To overcome them, several technologies have been developed, aiming for improved functionality, prolonged circulation time, enhanced proteolytic stability and bioavailability, and efficient and controlled delivery and release of defensins to the site of infection. Additional challenges include the alleviation of potential toxicity of defensins and their cost-effective manufacturing. In this review, we briefly introduce defensin biology, focus on various transforming strategies and practical techniques developed for defensins and their derivatives as antibacterial therapeutics, and conclude with a summation of future challenges and possible solutions.

The vaginal microbiota and innate immunity after local excisional treatment for cervical intraepithelial neoplasia

BACKGROUND

Vaginal microbiota (VMB) composition is altered in women with cervical intra-epithelial neoplasia (CIN) compared to healthy controls and is associated with disease progression. However, the impact of CIN excision on the VMB and innate immunity is not known. This observational study aims to explore the impact of CIN excision on the VMB, antimicrobial peptides (AMP) and proinflammatory cytokines.

METHODS

We sampled 103 non-pregnant, premenopausal women at the time of excisional treatment for CIN and at their 6-month follow-up visit. A further 39 untreated controls with normal cytology were also sampled. We used metataxonomics to group vaginal swab samples into community state types (CSTs) and ELISA to quantify cytokine and AMP levels in matched vaginal secretions. Analyses were performed to compare the bacterial composition and immune analyte levels before and after CIN excision and in healthy controls.

RESULTS

Women with CIN had significantly higher rates of Lactobacillus species depletion pre-treatment compared to healthy controls (CST IV 21/103, 20% vs 1/39, 3%, p = 0.0081). Excision did not change the VMB composition, with CST IV remaining significantly more prevalent after excision compared to untreated, healthy controls (CST IV 19/103, 20% vs 1/39, 3%, p = 0.0142). Prevotella bivia and Sneathia amnii were significantly higher in samples before treatment compared to untreated controls, and Prevotella bivia remained significantly higher amongst the treated, with less Lactobacillus crispatus compared to untreated controls. IL-1β and IL-8 remained significantly elevated pre- (p < 0.0001 and p = 0.0014, respectively) and post-treatment (p < 0.0001 and p = 0.0035, respectively) compared to untreated controls. Levels of human beta-defensin-1 and secretory leukocyte protease inhibitor were both significantly reduced following CIN excision (p < 0.0001); however, their levels remained lower than controls post-treatment.

CONCLUSIONS

Women with CIN have an increased prevalence of Lactobacillus sp. depletion, high-diversity VMB composition, and higher levels of proinflammatory cytokines and AMPs compared to normal controls. Surgical excision of the disease reduces levels of vaginal AMPs but does not alter VMB composition or cytokine levels. These findings suggest that women with CIN have an inherent predisposition to a high-diversity proinflammatory environment that is not corrected by disease excision. The failure to re-establish a Lactobacillus-enriched CST may explain why women remain at high risk of pre-invasive and invasive disease recurrence.

Chemotactic effect of β-defensin 1 on macrophages in Megalobrama amblycephala

Besides their function as a physical barrier against pathogens, β-defensins possess the ability to induce direct or indirect chemotaxis in leukocytes of mammals. However little is known about the ability of defensins to guide the migration of macrophages in fish. The objective of our study was to investigate whether β-defensin 1 (maBD1) can recruit leukocytes (specifically macrophages) in vivo and in vitro in a farmed cyprinid fish Megalobrama amblycephala. The M. amblycephala β-defensin 1 (maBD1) gene was amplified from the head-kidney transcriptome. Synthetic maBD1 polypeptide (as well as its N-terminus half, but not the C-terminus half) was capable of inducing the migration of leukocytes (specifically macrophages) at concentrations from 26.0 μg/mL to 52.0 μg/mL in head kidney tissue in vitro. When injected intraperitoneally in vivo, the number of leukocytes in the peritoneal cavity was in positive correlation with the maBD1 concentration. maBD1 also induced the expression of two proinflammatory cytokines (IL-1beta and TNF-alpha) in spleen, head and body kidney, and hepatopancreas. These results strongly indicate that BD1 has a chemoattractant capacity for macrophages, as well as the ability to modulate the expression of proinflammatory cytokines in fish.

Prediction of the impact of coding missense and nonsense single nucleotide polymorphisms on HD5 and HBD1 antibacterial activity against Escherichia coli

Defensins confer host defense against microorganisms and are important for human health. Single nucleotide polymorphisms (SNPs) in defensin gene-coding regions could lead to less active variants. Using SNP data available at the dbSNP database and frequency information from the 1000 Genomes Project, two DEFA5 (L26I and R13H) and eight DEFB1 (C35S, K31T, K33R, R29G, V06I, C12Y, Y28* and C05*) missense and nonsense SNPs that are located within mature regions of the coded defensins were retrieved. Such SNPs are rare and population restricted. In order to assess their antibacterial activity against Escherichia coli, two linear regression models were used from a previous work, which models the antibacterial activity as a function of solvation potential energy, using molecular dynamics data. Regarding only the antibacterial predictions, for HD5, no biological differences between wild-type and its variants were observed; while for HBD1, the results suggest that the R29G, K31T, Y28* and C05* variants could be less active than the wild-type one. The data here reported could lead to a substantial improvement in knowledge about the impact of missense SNPs in human defensins and their world distribution. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 633-644, 2016.

FAD-I, a Fusobacterium nucleatum Cell Wall-Associated Diacylated Lipoprotein That Mediates Human Beta Defensin 2 Induction through Toll-Like Receptor-1/2 (TLR-1/2) and TLR-2/6

We previously identified a cell wall-associated protein from Fusobacterium nucleatum, a Gram-negative bacterium of the oral cavity, that induces human beta defensin 2 (hBD-2) in primary human oral epithelial cells (HOECs) and designated it FAD-I (Fusobacterium-associated defensin inducer). Here, we report differential induction of hBD-2 by different strains of F. nucleatum; ATCC 25586 and ATCC 23726 induce significantly more hBD-2 mRNA than ATCC 10953. Heterologous expression of plasmid-borne fadI from the highly hBD-2-inducing strains in a ΔfadI mutant of ATCC 10953 resulted in hBD-2 induction to levels comparable to those of the highly inducing strains, indicating that FAD-I is the principal F. nucleatum agent for hBD-2 induction in HOECs. Moreover, anti-FAD-I antibodies blocked F. nucleatum induction of hBD-2 by more than 80%. Recombinant FAD-I (rFAD-I) expressed in Escherichia coli triggered levels of hBD-2 transcription and peptide release in HOECs similar to those of native FAD-I (nFAD-I) isolated from F. nucleatum ATCC 25586. Tandem mass spectrometry revealed a diacylglycerol modification at the cysteine residue in position 16 for both nFAD-I and rFAD-I. Cysteine-to-alanine substitution abrogated FAD-I's ability to induce hBD-2. Finally, FAD-I activation of hBD-2 expression was mediated via both Toll-like receptor-1/2 (TLR-1/2) and TLR-2/6 heterodimerization. Microbial molecules like FAD-I may be utilized in novel therapeutic ways to bolster the host innate immune response at mucosal surfaces.

An intimate link between antimicrobial peptide sequence diversity and binding to essential components of bacterial membranes

Antimicrobial peptides and proteins (AMPs) are widespread in the living kingdom. They are key effectors of defense reactions and mediators of competitions between organisms. They are often cationic and amphiphilic, which favors their interactions with the anionic membranes of microorganisms. Several AMP families do not directly alter membrane integrity but rather target conserved components of the bacterial membranes in a process that provides them with potent and specific antimicrobial activities. Thus, lipopolysaccharides (LPS), lipoteichoic acids (LTA) and the peptidoglycan precursor Lipid II are targeted by a broad series of AMPs. Studying the functional diversity of immune effectors tells us about the essential residues involved in AMP mechanism of action. Marine invertebrates have been found to produce a remarkable diversity of AMPs. Molluscan defensins and crustacean anti-LPS factors (ALF) are diverse in terms of amino acid sequence and show contrasted phenotypes in terms of antimicrobial activity. Their activity is directed essentially against Gram-positive or Gram-negative bacteria due to their specific interactions with Lipid II or Lipid A, respectively. Through those interesting examples, we discuss here how sequence diversity generated throughout evolution informs us on residues required for essential molecular interaction at the bacterial membranes and subsequent antibacterial activity. Through the analysis of molecular variants having lost antibacterial activity or shaped novel functions, we also discuss the molecular bases of functional divergence in AMPs. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Modification of β-Defensin-2 by Dicarbonyls Methylglyoxal and Glyoxal Inhibits Antibacterial and Chemotactic Function In Vitro

Background

Beta-defensins (hBDs) provide antimicrobial and chemotactic defense against bacterial, viral and fungal infections. Human β-defensin-2 (hBD-2) acts against gram-negative bacteria and chemoattracts immature dendritic cells, thus regulating innate and adaptive immunity. Immunosuppression due to hyperglycemia underlies chronic infection in Type 2 diabetes. Hyperglycemia also elevates production of dicarbonyls methylgloxal (MGO) and glyoxal (GO).

Methods

The effect of dicarbonyl on defensin peptide structure was tested by exposing recombinant hBD-2 (rhBD-2) to MGO or GO with subsequent analysis by MALDI-TOF MS and LC/MS/MS. Antimicrobial function of untreated rhBD-2 vs. rhBD-2 exposed to dicarbonyl against strains of both gram-negative and gram-positive bacteria in culture was determined by radial diffusion assay. The effect of dicarbonyl on rhBD-2 chemotactic function was determined by chemotaxis assay in CEM-SS cells.

Results

MGO or GO in vitro irreversibly adducts to the rhBD-2 peptide, and significantly reduces antimicrobial and chemotactic functions. Adducts derive from two arginine residues, Arg²² and Arg²³ near the C-terminus, and the N-terminal glycine (Gly¹). We show by radial diffusion testing on gram-negative E. coli and P. aeruginosa, and gram-positive S. aureus, and a chemotaxis assay for CEM-SS cells, that antimicrobial activity and chemotactic function of rhBD-2 are significantly reduced by MGO.

Conclusions

Dicarbonyl modification of cationic antimicrobial peptides represents a potential link between hyperglycemia and the clinical manifestation of increased susceptibility to infection, protracted wound healing, and chronic inflammation in undiagnosed and uncontrolled Type 2 diabetes.

Peptides and Peptidomimetics for Antimicrobial Drug Design

The purpose of this paper is to introduce and highlight a few classes of traditional antimicrobial peptides with a focus on structure-activity relationship studies. After first dissecting the important physiochemical properties that influence the antimicrobial and toxic properties of antimicrobial peptides, the contributions of individual amino acids with respect to the peptides antibacterial properties are presented. A brief discussion of the mechanisms of action of different antimicrobials as well as the development of bacterial resistance towards antimicrobial peptides follows. Finally, current efforts on novel design strategies and peptidomimetics are introduced to illustrate the importance of antimicrobial peptide research in the development of future antibiotics.

Chronic tonsillitis is not associated with beta defensin 1 gene polymorphisms in Turkish population

BACKGROUND

Defensins are antimicrobial peptides expressed on mucosal surfaces. They function as part of the innate immune system. Palatine tonsils play important roles in innate immune system. However, our knowledge on the pathophysiology of chronic tonsils is limited.

OBJECTIVE

The aim of this study was to investigate the association between beta defensin 1 gene single nucleotide polymorphisms and chronic tonsillitis.

STUDY DESIGN

Prospective, non-randomized, controlled clinical study.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

Eighty six patients with chronic tonsillitis and eighty controls without history of chronic tonsillitis were enrolled in this study. Genotypes were determined by restriction fragment length polymorphism analyses after polymerase chain reaction.

RESULTS

Genotype and allele frequencies of the -20G/A (rs11362), -44C/G (rs1800972) and -52G/A (rs1799946) single nucleotide polymorphisms were not statistically different between patients and control groups (p>0.05).

CONCLUSION

In this study, we found that DEFB1 gene -20G/A, -44C/G and -52G/A single nucleotide polymorphisms were not associated with chronic tonsillitis. Studies, which analyse other polymorphism of the beta defensin 1 gene in large case series, should be conducted to understand the role of DEFB1 gene on chronic tonsillitis.

Antimicrobial characterization of site-directed mutagenesis of porcine beta defensin 2

Porcine β defensin 2 (pBD2) is a small, cationic and amphiphilic antimicrobial peptide. It has broad antimicrobial activities against bacteria and plays an important role in host defense. In order to enhance its antimicrobial activity and better understand the effect of positively charged residues on its activity, we substituted eight amino acid residues with arginine or lysine respectively. All mutants were cloned and expressed in BL21 (DE3) plysS and the mutant proteins were then purified. These mutant versions had higher positive charges but similar structural configurations compared to the wild-type pBD2. Moreover, these mutant proteins showed different antimicrobial activities against E. coli and S. aureus. The mutant I4R of pBD2 had the highest antimicrobial activity. In addition, all the mutants showed low hemolytic activities. Our results indicated that the positively charged residues were not the only factor that influenced antimicrobial activity, but other factors such as distribution of these residues on the surface of defensins might also contribute to their antimicrobial potency.

Delineation of interfaces on human alpha-defensins critical for human adenovirus and human papillomavirus inhibition

Human α-defensins are potent anti-microbial peptides with the ability to neutralize bacterial and viral targets. Single alanine mutagenesis has been used to identify determinants of anti-bacterial activity and binding to bacterial proteins such as anthrax lethal factor. Similar analyses of α-defensin interactions with non-enveloped viruses are limited. We used a comprehensive set of human α-defensin 5 (HD5) and human neutrophil peptide 1 (HNP1) alanine scan mutants in a combination of binding and neutralization assays with human adenovirus (AdV) and human papillomavirus (HPV). We have identified a core of critical hydrophobic residues that are common determinants for all of the virus-defensin interactions that were analyzed, while specificity in viral recognition is conferred by specific surface-exposed charged residues. The hydrophobic residues serve multiple roles in maintaining the tertiary and quaternary structure of the defensins as well as forming an interface for virus binding. Many of the important solvent-exposed residues of HD5 group together to form a critical surface. However, a single discrete binding face was not identified for HNP1. In lieu of whole AdV, we used a recombinant capsid subunit comprised of penton base and fiber in quantitative binding studies and determined that the anti-viral potency of HD5 was a function of stoichiometry rather than affinity. Our studies support a mechanism in which α-defensins depend on hydrophobic and charge-charge interactions to bind at high copy number to these non-enveloped viruses to neutralize infection and provide insight into properties that guide α-defensin anti-viral activity.

Human α-defensins are an important component of the innate immune response and provide an initial block against a broad number of infectious agents, including viruses and bacteria. Characteristics of α-defensins that are necessary for their anti-bacterial activity have been identified, but our understanding of determinants required for activity against non-enveloped viruses is limited. In this work, we utilized alanine scan mutagenesis to systematically and comprehensively investigate the role of hydrophobic and charged residues of two α-defensins in binding to and/or neutralization of human adenovirus and human papillomavirus. Our results implicate common core hydrophobic residues as critical for inhibition of these non-enveloped viruses by the two α-defensins, with specificity provided by charged residues unique to each interaction. We also found that the number of α-defensin molecules bound to the virus was a stronger correlate of the anti-viral potency of the α-defensin mutants than their absolute affinity for the viral capsid. Understanding common characteristics of α-defensins important for non-enveloped virus binding will inform rules that govern the function of these abundant and multifaceted peptides in host defense.

Molecular and functional analysis of human β-defensin 3 action at melanocortin receptors

The β-defensins are a class of small, cationic proteins first recognized as antimicrobial components of the innate and adaptive immune system. More recently, one of the major β-defensins produced in skin, β-defensin 3, has been discovered to function as a melanocortin receptor ligand in vivo and in vitro, but its biophysical and pharmacological basis of action has been enigmatic. Here, we report functional and biochemical studies focused on human β-defensin 3 (HBD3) and melanocortin receptors 1 and 4. Genetic and pharmacologic studies indicate that HBD3 acts as a neutral melanocortin receptor antagonist capable of blocking the action of either stimulatory agonists such as α-melanocyte stimulating hormone or inhibitory inverse agonists such as Agouti signaling protein (ASIP) and Agouti-related protein (AGRP). A comprehensive structure-function analysis demonstrates that two patches of positively charged residues, located on opposite poles of HBD3 and spatially organized by the compact β-defensin fold, are primarily responsible for high-affinity binding to melanocortin receptors. These findings identify a distinct mode of melanocortin receptor-ligand interactions based primarily on electrostatic complementarity, with implications for designing ligands that target melanocortin and potentially other seven transmembrane receptors.

Antimicrobial peptide β-defensin-1 expression is upregulated in Alzheimer's brain

Background

The human β-defensins (hBDs) are a highly conserved family of cationic antimicrobial and immunomodulatory peptides expressed primarily by epithelial cells in response to invasion by bacteria, fungi and some viruses. To date, the most studied members of this family of peptides are hBD-1, -2, and -3. Expression of hBD-1 and -2 has been demonstrated previously in cultured microglia and astrocytes of both mouse and human brain. Unlike inducible hBD-2 and -3, hBD-1 is constitutively expressed and is not generally upregulated by proinflammatory factors. In this study, we investigated whether hBDs, as active components of the innate immune response, are affected by pathological events in the Alzheimer’s disease (AD) brain. We assessed the expression of hBD-1, -2, and -3 in tissue obtained at autopsy from AD and age-matched control brains.

Methods

Fixed and frozen choroid plexus and the CA1 region of the hippocampus were obtained at autopsy from individuals diagnosed with AD, or from age-matched control brains without diagnosed neurodegenerative disease. Histopathologically diagnosed AD brain tissue was obtained for our study. Immunocytochemical analysis was performed using affinity purified polyclonal antibodies directed against hBD-1, -2, or -3. TaqMan gene expression assays were used to quantify the mRNA of hBD-1, -2, and -3 in the choroid plexus and hippocampus. Immunocytochemical detection of iron deposits was achieved using a modified Perl’s stain for redox-active iron. In vitro experiments were performed on human primary oral epithelial cells to model the human choroid plexus epithelial response to ferric chloride. Cells were then exposed to ferric chloride added to selected wells at 0, 1, or 10 mM concentrations for 24 h at 37°C. Total mRNA was isolated to quantify hBD-1 mRNA expression by RTqPCR.

Results

hBD-1 peptide is apparent in astrocytes of the AD hippocampus and hippocampal neurons, notably within granulovacuolar degeneration structures (GVD). A higher level of hBD-1 was also seen in the choroid plexus of AD brain in comparison to age-matched control tissue. Increased expression of hBD-1 mRNA was observed only in the choroid plexus of the AD brain when compared to expression level in age-matched control brain. Redox-active iron was also elevated in the AD choroid plexus and in vitro addition of Fe⁺³Cl₃ to cultured epithelial cells induced hBD-1 mRNA expression.

Conclusions

Our findings suggest interplay between hBD-1 and neuroimmunological responses in AD, marked by microglial and astrocytic activation, and increased expression of the peptide within the choroid plexus and accumulation within GVD. As a constitutively expressed component of the innate immune system, we propose that hBD-1 may be of considerable importance early in the disease process. We also demonstrate that increased iron deposition in AD may contribute to the elevated expression of hBD-1 within the choroid plexus. These findings represent a potentially important etiological aspect of Alzheimer’s disease neuropathology not previously reported.

Sequence polymorphism and expression variability of Crassostrea gigas immune related genes discriminate two oyster lines contrasted in term of resistance to summer mortalities

Summer mortalities of Crassostreagigas are a major concern in oyster aquaculture. They are the result of a complex interaction between the host, pathogens and environmental factors. Oyster genetics have been identified as an essential determinant of oyster susceptibility to summer mortalities. As the capability of oysters to circumvent diseases depends in part on their immune defenses, we aimed to analyze the gene expression and sequence polymorphism of 42 immune related genes in two oyster lines selected for their “High” (H) and “Low” (L) survival to summer mortalities. Results showed that the variability of gene expression and the sequence polymorphism acting on particular genes could enable the discrimination between H and L oyster lines. Besides, a higher sequence polymorphism was observed on the L line affecting 11 of the 42 analyzed genes. By analyzing gene expression, sequence polymorphism and gene copy number of two antimicrobial peptide families (Cg-Defs and Cg-Prp), and an antimicrobial protein (Cg-BPI) on individual oysters, we showed that gene expression and/or sequence polymorphism could also discriminate H and L oyster lines. Finally, we observed a positive correlation between the gene expression and the gene copy number of antimicrobials and that sequence polymorphism could be encoded in the genome. Overall, this study gives new insights in the relationship between oyster immunity and divergent phenotypes, and discusses the potential implication of antimicrobial diversity in oyster survival to summer mortalities.

Human-β-defensins-1-3 and analogs do not require proton motive force for antibacterial activity against Escherichia coli

Human-β-defensins 1-3 (HBD-1-3) and their C-terminal analogs Phd-1-3 do not show antibacterial activity against Escherichia coli in the presence of mono- and divalent cations. Activity of peptides was examined against E. coli pretreated with carbonyl cyanide m-chlorophenylhydrazone (CCCP) and salt remedial Escherichia coli ftsEX, a deletion mutant of FtsEX complex [an ATP-binding cassette (ABC) transporter protein], in the presence of Na(+), Ca(2+), and Mg(2+). Activity was observed in the presence of Na(+) and Ca(2+), although not in the presence of Mg(2+) against E. coli, when proton motive force (PMF) was dissipated by CCCP. The peptides exhibited antibacterial activity against E. coli ftsEX even in the presence of Na(+) and Ca(2+). Our results indicate that HBD-1-3 and Phd-1-3 do not require PMF for their antibacterial activity. The absence of activity against E. coli in the presence of Na(+) and Ca(2+) ions is due to not only weakened electrostatic interactions with anionic membrane components, but also involvement of electrochemical gradients. However, Mg(2+) prevents electrostatic interaction of the peptides with the outer membrane resulting in loss of activity.

Structural basis for the interaction of human β-defensin 6 and its putative chemokine receptor CCR2 and breast cancer microvesicles

Human β-defensins (hBDs) are believed to function as alarm molecules that stimulate the adaptive immune system when a threat is present. In addition to its antimicrobial activity, defensins present other activities such as chemoattraction of a range of different cell types to the sites of inflammation. We have solved the structure of the hBD6 by NMR spectroscopy that contains a conserved β-defensin domain followed by an extended C-terminus. We use NMR to monitor the interaction of hBD6 with microvesicles shed by breast cancer cell lines and with peptides derived from the extracellular domain of CC chemokine receptor 2 (Nt-CCR2) possessing or not possessing sulfation on Tyr26 and Tyr28. The NMR-derived model of the hBD6/CCR2 complex reveals a contiguous binding surface on hBD6, which comprises amino acid residues of the α-helix and β2-β3 loop. The microvesicle binding surface partially overlaps with the chemokine receptor interface. NMR spin relaxation suggests that free hBD6 and the hBD6/CCR2 complex exhibit microsecond-to-millisecond conformational dynamics encompassing the CCR2 binding site, which might facilitate selection of the molecular configuration optimal for binding. These data offer new insights into the structure-function relation of the hBD6-CCR2 interaction, which is a promising target for the design of novel anticancer agents.

Expression of β-defensin 4 on temporomandibular joint discs with anterior displacement without reduction

OBJECTIVES

β-defensin-4 is a member of antimicrobial peptides (APs) of the immunity system. This molecule has antimicrobial activity but it seems to be involved in articular inflammatory processes too, as it happens during osteoarthritic disease (OA). Considering the possible relation existing between (OA) and temporomandibular disorders (TMD), the aim of our study was to evaluate immunohistochemically the presence of β- defensin-4 in pathological temporomandibular joint (TMJ) discs affected by internal derangement without reduction (ADDwoR).

DESIGN

Eighteen TMJ-displaced disc specimens were considered in this study and were analysed by immunohistochemical evaluation. They were compared with a control sample of sixteen healthy discs and two scores, intensity of staining (IS) and extent score (ES) were estimated.

RESULTS

Findings of our analysis showed a significant difference between control and study sample (P < 0.001). IS and ES of control sample and pathological sample were 1 and 4 respectively.

CONCLUSION

Our results confirmed the presence of β-defensin-4 in human TMJ discs affected by ADDwoR, hypothesing a possible role of this molecule in articular bone disruption.

Antimicrobial activity of human β-defensin 4 analogs: insights into the role of disulfide linkages in modulating activity

Human β-defensins (HBDs) are cationic antimicrobial peptides that are components of the innate immune system. They are characterized by three disulfide bridges. However, the number of cationic residues as well as the presence of lysine and arginine residues vary. In HBD4, the cationic residues occur predominantly in the N-terminal segment, unlike in HBD1-3. We have examined the antimicrobial activity of peptides spanning the N- and C-terminal segments of HBD4. We have introduced one, two and three disulfide bridges in the peptides corresponding to the N-terminal segments. Peptides corresponding to the N-terminal segment had identical sequences and variation was only in the number and spacing of cysteines and disulfide bridges. Antimicrobial activity to varying extents was observed for all the peptides. When two disulfide bridges were present, decrease in antimicrobial potency as well as sensitivity of activity to salt was observed. Enhanced antimicrobial activity was observed when three disulfide bridges were present. The antimicrobial potency was similar to HBD4 except against Escherichia coli and was attenuated in the presence of salt. While the presence of three disulfide bridges did not constrain the peptide to a rigid β-sheet, the activity was considerably more as compared to the peptides with one or two disulfide bridges. The peptides enter bacterial and fungal cells rapidly without membrane permeabilization and appear to exert their activity inside the cells rather than at the membrane.

Inflammatory bowel disease: an impaired barrier disease

BACKGROUND

The intestinal barrier is a delicate structure composed of a single layer of epithelial cells, the mucus, commensal bacteria, immune cells, and antibodies. Furthermore, a wealth of antimicrobial peptides (AMPs) can be found in the mucus and defend the mucosa. Different lines of investigations now point to a prominent pathophysiological role of defensins, an important family of AMPs, in the pathogenesis of inflammatory bowel disease and, particularly, in small intestinal Crohn's disease.

PURPOSE

In this review, we introduce the different antimicrobial peptides of the intestinal mucosa and describe their function, their expression pattern along the gastrointestinal tract, and their spatial relationship to the mucus layer. We then focus on the alterations found in inflammatory bowel disease. Small intestinal Crohn's disease (CD) is closely linked to defects in Paneth cells (specialized secretory epithelial cells at the bottom crypts) which secrete α-defensin human defensin (HD)-5 in huge quantities in healthy individuals. Decreased expression of these antimicrobial peptides is found in ileal CD, and single nucleotide polymorphisms with the highest linkage to CD affect genes involved in Paneth cell biology and defensin secretion. Additionally, antimicrobial peptides have a role in ulcerative colitis, where the depleted mucus layer cannot fulfill its crucial function of binding defensins and other AMPs to their proper site of action.

CONCLUSION

Inflammatory bowel disease arises when the mucosal barrier is compromised in its defense against challenges from the intestinal microbiota. In ileal CD, a strong association can be found between diminished expression or defective function of defensins and the advent of intestinal inflammation.

Defensin like peptide from Panulirus argus relates structurally with beta defensin from vertebrates

Naturally occurring antimicrobial peptides take place in the first line of host defense against pathogen as part of the humoral innate immune response. β-defensins are among the most abundant antimicrobial peptides in mammals, and thought to be solely found in vertebrates until a recent report describing the cloning and sequencing of defensin like peptides in the spiny lobster Panulirus japonicus. In the current study, we cloned and sequenced two genes from the hemocytes of the spiny lobster Panulirus argus encoding for two isoforms of defensin-like peptides, thus confirming the presence of this protein in the Panulirus genus. The 44 amino acids mature peptides showed the conservation of cysteine pattern characterizing the β-defensins, as well as known amino acids residues critical to exert their antimicrobial activity. They are also amphipathics, hydrophobics, and display an overall positive charge (+1) located at the C-terminus. The tertiary structure obtained by homology modeling indicated that likely conformations of lobster peptides are highly similar to β-defensins from vertebrates. The phylogenetic study carried out by probabilistic methods confirmed the relation with ancestral β-defensin from vertebrates. The finding of a putative defensin-like peptide in the expressed sequence tag (EST) of the lobster Homarus americanus with high homology with those of P. argus described in this study, would indicate the presence of this peptides in Palinuridae family. Taking into account all similarities between these peptides with β-defensins from vertebrates, it is conceivable to further support the finding of a new family of β-defensins in invertebrate.

Dimerization of plant defensin NaD1 enhances its antifungal activity

The plant defensin, NaD1, from the flowers of Nicotiana alata, is a member of a family of cationic peptides that displays growth inhibitory activity against several filamentous fungi, including Fusarium oxysporum. The antifungal activity of NaD1 has been attributed to its ability to permeabilize membranes; however, the molecular basis of this function remains poorly defined. In this study, we have solved the structure of NaD1 from two crystal forms to high resolution (1.4 and 1.58 Å, respectively), both of which contain NaD1 in a dimeric configuration. Using protein cross-linking experiments as well as small angle x-ray scattering analysis and analytical ultracentrifugation, we show that NaD1 forms dimers in solution. The structural studies identified Lys(4) as critical in formation of the NaD1 dimer. This was confirmed by site-directed mutagenesis of Lys(4) that resulted in substantially reduced dimer formation. Significantly, the reduced ability of the Lys(4) mutant to dimerize correlated with diminished antifungal activity. These data demonstrate the importance of dimerization in NaD1 function and have implications for the use of defensins in agribiotechnology applications such as enhancing plant crop protection against fungal pathogens.

Streptococcus pyogenes infection of tonsil explants is associated with a human β-defensin 1 response from control but not recurrent acute tonsillitis patients

Host defence peptides (HDP), including the defensins and hCAP-18, function as part of the innate immune defences, protecting the host epithelia from microbial attachment and invasion. Recurrent acute tonsillitis (RAT), in which patients suffer repeated symptomatic tonsil infections, is linked to Streptococcus pyogenes, a group A streptococcus, and may reflect the impaired expression of such peptides. To address this, the defensin and hCAP-18 messenger RNA expression profiles of 54 tonsils excised from control and RAT patients undergoing tonsillectomy were quantified and compared. Marked variation in expression was observed between individuals from the two groups, but statistically no significant differences were identified, suggesting that at the time of surgery the tonsil epithelial HDP barrier was not compromised in RAT subjects. Surgical removal of the tonsils occurs in a quiescent phase of disease, and so to assess the effects of an active bacterial infection, HaCaT cells an in vitro model of the tonsil epithelium, and explants of patient tonsils maintained in vitro were challenged with S. pyogenes. The HaCaT data supported the reduced expression of hCAP-18/LL-37, human β-defensin 1 (HBD1;P < 0.01) and HBD2 (P < 0.05), consistent with decreased protection of the epithelial barrier. The tonsil explant data, although not as definitive, showed similar trends apart from HBD1 expression, which in the control tonsils but not the RAT patient tonsils was characterized by increased expression (P < 0.01). These data suggest that in vivo HBD1 may play a critical role in protecting the tonsil epithelia from S. pyogenes.

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

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

Effects on antigen-presenting cells of short-term interaction with the human host defence peptide β-defensin 2

β-Defensins are antimicrobial peptides that exert their host-defence functions at the interface between the host and microbial biota. They display a direct, salt- and medium-sensitive cidal activity, in vitro, against a broad spectrum of bacteria and fungi, and there is increasing evidence that they also play a role in alerting and enhancing cellular components of innate and adaptive immunity. Their interaction with biological membranes plays a central role in both of these types of activities. In the present study, we have investigated the interaction of fluorescently labelled hBD2 (human β-defensin 2) with monocytes, macrophages and iDCs (immature dendritic cells), observing a differential capacity to be rapidly internalized into these cells. Complementary microscopy techniques [TEM (transmission electron microscopy), optical microscopy and IR microspectroscopy] were used to explore the functional and biological implications of these interactions on iDCs. Short-term exposure to the peptide resulted in significant alterations in membrane composition and re-organization of the endomembrane system, with the induction of degranulation. These events may be associated with the antigen-presenting activities or the chemotaxis of iDCs, which appears to occur via both CCR6 (CC chemokine receptor 6)-dependent and -independent mechanisms.

Importance of residue 13 and the C-terminus for the structure and activity of the antimicrobial peptide aurein 2.2

Previous studies on aurein 2.2 and 2.3 in DMPC/DMPG and POPC/POPG membranes have shown that bilayer thickness and phosphatidylglycerol content have a significant impact on the interaction of these peptides with membrane bilayers. Further examination with the DiSC(3)5 assay has indicated that aurein 2.2 induces greater membrane leakage than aurein 2.3 in Staphylococcus aureus C622. The only difference between these peptides is a Leu to Ile mutation at residue 13. To better understand the importance of this residue, the structure and activity of the L13A, L13F, and L13V mutants were investigated. In addition, we investigated a number of peptides with truncations at the C-terminus to determine whether the C-terminus, which contains residue 13, is crucial for antimicrobial activity. Solution circular dichroism results demonstrated that the L13F mutation and the truncation of the C-terminus by six residues resulted in decreased helical content, whereas the L13A or L13V mutation and the truncation of the C-terminus by three residues showed little to no effect on the structure. Oriented circular dichroism results demonstrated that only an extensive C-terminal truncation reduced the ability of the peptide to insert into lipid bilayers. (31)P NMR spectroscopy showed that all peptides disorder the headgroups. The implications of these results in terms of antimicrobial activity and the ability of these peptides to induce leakage in S. aureus are discussed. The results suggest that the presence of the 13th residue in aurein 2.2 is important for structure and activity, but the exact nature of residue 13 is less important as long as it is a hydrophobic residue.

Topical antimicrobials for burn wound infections

Throughout most of history, serious burns occupying a large percentage of body surface area were an almost certain death sentence because of subsequent infection. A number of factors such as disruption of the skin barrier, ready availability of bacterial nutrients in the burn milieu, destruction of the vascular supply to the burned skin, and systemic disturbances lead to immunosuppression combined together to make burns particularly susceptible to infection. In the 20th century the introduction of antibiotic and antifungal drugs, the use of topical antimicrobials that could be applied to burns, and widespread adoption of early excision and grafting all helped to dramatically increase survival. However the relentless increase in microbial resistance to antibiotics and other antimicrobials has led to a renewed search for alternative approaches to prevent and combat burn infections. This review will cover patented strategies that have been issued or filed with regard to new topical agents, preparations, and methods of combating burn infections. Animal models that are used in preclinical studies are discussed. Various silver preparations (nanocrystalline and slow release) are the mainstay of many approaches but antimicrobial peptides, topical photodynamic therapy, chitosan preparations, new iodine delivery formulations, phage therapy and natural products such as honey and essential oils have all been tested. This active area of research will continue to provide new topical antimicrobials for burns that will battle against growing multidrug resistance.

Conformational preferences of linear beta-defensins are revealed by ion mobility-mass spectrometry

In recent times there has been an enormous rise in resistance to synthetic antibiotics as well as an increase in the virulence of bacteria, the so-called "superbugs". This problem has catalyzed a search for novel molecules to fight bacteria, which in turn relies on a better understanding of the molecular basis of the immune response. Beta-defensins are a class of small, cationic, cysteine-rich antimicrobial peptides expressed by humans and other animals to act against incoming pathogens. As well as their antimicrobial properties, beta-defensins also act as chemokines, recruiting cells to the sites of infection. Here the relationship between the tertiary structures of beta-defensin analogs and their chemotactic activities has been investigated using ion mobility-mass spectrometry (IM-MS) and biochemical assays. A panel of derivatives of the murine beta-defensin Defb14 has been formed and the ability of these peptides to chemoattract the receptor CCR6 has been assessed in vitro. The derivatives can be divided into two groups, those with chemotactic activity equal to that of the unmodified parent peptide, and those whose chemotactic activity has been lost upon modification. Analysis by ion mobility-mass spectrometry reveals the conformational preferences of these peptides upon ionization from different solvents. Under denaturing conditions, the chemotactic peptides adopt more compact conformations in the gas-phase at higher charge states than those which are inactive. While the conditions of these experiments are not akin to the environment around the receptor in vivo, this technique provides an in vacuo method for distinguishing between the different chemotactic activities of beta-defensin derivatives.

Peptide fragments of a beta-defensin derivative with potent bactericidal activity

Beta-defensins are known to be both antimicrobial and able to chemoattract various immune cells. Although the sequences of paralogous genes are not highly conserved, the core defensin structure is retained. Defb14-1C(V) has bactericidal activity similar to that of its parent peptide (murine beta-defensin Defb14) despite all but one of the canonical six cysteines being replaced with alanines. The 23-amino-acid N-terminal half of Defb14-1C(V) is a potent antimicrobial while the C-terminal half is not. Here, we use a library of peptide derivatives to demonstrate that the antimicrobial activity can be localized to a particular region. Overlapping fragments of the N-terminal region were tested for their ability to kill Gram-positive and Gram-negative bacteria. We demonstrate that the most N-terminal fragments (amino acids 1 to 10 and 6 to 17) are potent antimicrobials against Gram-negative bacteria whereas fragments based on sequence more C terminal than amino acid 13 have very poor activity against both Gram-positive and -negative types. We further test a series of N-terminal deletion peptides in both their monomeric and dimeric forms. We find that bactericidal activity is lost against both Gram types as the deletion region increases, with the point at which this occurs varying between bacterial strains. The dimeric form of the peptides is more resistant to the peptide deletions, but this is not due just to increased charge. Our results indicate that the primary sequence, together with structure, is essential in the bactericidal action of this beta-defensin derivative peptide and importantly identifies a short fragment from the peptide that is a potent bactericide.

Molecular diversity of antimicrobial effectors in the oyster Crassostrea gigas

Background

To gain insight into the molecular diversity of antimicrobial peptides and proteins in the oyster Crassostrea gigas, we characterized and compared the sequence polymorphism of the antimicrobial peptides (AMPs), Cg-Defensins (Cg-Defs) and Cg-Proline Rich peptide (Cg-Prp), and of the bactericidal permeability increasing protein, Cg-BPI. For that, we analyzed genomic and transcript sequences obtained by specific PCR amplification and in silico searches.

Results

High diversification among the three antimicrobial effectors was evidenced by this polymorphism survey. On the basis of sequence phylogenies, each AMP aggregates into clearly defined groups of variants and is the product of a multigenic family displaying a variety of gene structures. In contrast, Cg-bpi forms a single group and is encoded by a single gene copy. Moreover, we identified for both AMPs several genetic mechanisms of diversification such as recombination, parallel mutations leading to phylogenetic homoplasy and indel events. In addition, the non synonymous to synonymous substitutions ratio by codon (dN/dS) revealed several negatively and positively selected sites for both AMPs, suggesting that directional selection pressures have shaped their sequence variations.

Conclusions

This study shows for the first time in a mollusc that antimicrobial peptides and proteins have been subject to distinct patterns of diversification and we evidence the existence of different evolutionary routes leading to such sequence variability.

The antimicrobial activity of CCL28 is dependent on C-terminal positively-charged amino acids

Several chemokines have been shown to act as antimicrobial proteins, suggesting a direct contribution to innate immune protection. Based on the study of defensins and other antimicrobial peptides, it has been proposed that cationic amino acids in these proteins play a key role in their antimicrobial activity. The primary structure requirements necessary for the antimicrobial activity of chemokines, however, have not yet been elucidated. Using mouse CCL28, we have identified a C-terminal region of highly-charged amino acids (RKDRK) that is essential to the antimicrobial activity of the murine chemokine. Additionally, other positively-charged amino acids in the C-terminus of the protein contribute to the observed antimicrobial effect. Charge reversal and deletion mutations support our hypothesis that C-terminal positively-charged amino acids are essential for the antimicrobial activity of CCL28. Results also demonstrate that although the C-terminal region of the chemokine is essential, it is not sufficient for full antimicrobial activity of CCL28.

Structure-function studies of chemokine-derived carboxy-terminal antimicrobial peptides

Recent reports which show that several chemokines can act as direct microbicidal agents have drawn renewed attention to these chemotactic signalling proteins. Here we present a structure-function analysis of peptides derived from the human chemokines macrophage inflammatory protein-3alpha (MIP-3alpha/CCL20), interleukin-8 (IL-8), neutrophil activating protein-2 (NAP-2) and thrombocidin-1 (TC-1). These peptides encompass the C-terminal alpha-helices of these chemokines, which have been suggested to be important for the direct antimicrobial activities. Far-UV CD spectroscopy showed that the peptides are unstructured in aqueous solution and that a membrane mimetic solvent is required to induce a helical secondary structure. A co-solvent mixture was used to determine solution structures of the peptides by two-dimensional (1)H-NMR spectroscopy. The highly cationic peptide, MIP-3alpha(51-70), had the most pronounced antimicrobial activity and displayed an amphipathic structure. A shorter version of this peptide, MIP-3alpha(59-70), remained antimicrobial but its structure and mechanism of action were unlike that of the former peptide. The NAP-2 and TC-1 proteins differ in their sequences only by the deletion of two C-terminal residues in TC-1, but intact TC-1 is a very potent antimicrobial while NAP-2 is inactive. The corresponding C-terminal peptides, NAP-2(50-70) and TC-1(50-68), had very limited and no bactericidal activity, respectively. This suggests that other regions of TC-1 contribute to its bactericidal activity. Altogether, this work provides a rational structural basis for the biological activities of these peptides and proteins and highlights the importance of experimental characterization of peptide fragments as distinct entities because their activities and structural properties may differ substantially from their parent proteins.

A theoretical approach to spot active regions in antimicrobial proteins

Background

Much effort goes into identifying new antimicrobial compounds able to evade the increasing resistance of microorganisms to antibiotics. One strategy relies on antimicrobial peptides, either derived from fragments released by proteolytic cleavage of proteins or designed from known antimicrobial protein regions.

Results

To identify these antimicrobial determinants, we developed a theoretical approach that predicts antimicrobial proteins from their amino acid sequence in addition to determining their antimicrobial regions. A bactericidal propensity index has been calculated for each amino acid, using the experimental data reported from a high-throughput screening assay as reference. Scanning profiles were performed for protein sequences and potentially active stretches were identified by the best selected threshold parameters. The method was corroborated against positive and negative datasets. This successful approach means that we can spot active sequences previously reported in the literature from experimental data for most of the antimicrobial proteins examined.

Conclusion

The method presented can correctly identify antimicrobial proteins with an accuracy of 85% and a sensitivity of 90%. The method can also predict their key active regions, making this a tool for the design of new antimicrobial drugs.

Artificial β-defensin based on a minimal defensin template

We have designed and chemically synthesized an artificial β-defensin based on a minimal template derived from the comparative analysis of over 80 naturally occurring sequences. This molecule has the disulfide-bridged β-sheet core structure of natural β-defensins and shows a robust salt-sensitive antimicrobial activity against bacteria and yeast, as well as a chemotactic activity against immature dendritic cells. An SAR (structure–activity relationship) study using two truncated fragments or a Cys→Ser point-mutated analogue, from which one or two of the three disulfide bridges were absent, indicated that altering the structure resulted in a different type of membrane interaction and a switch to different modes of action towards both microbial and host cells, and that covalent dimerization could favour antimicrobial activity. Comparison of the structural, aggregational and biological activities of the artificial defensin with those of three human β-defensins and their primate orthologues provided useful information on how their mode of action may relate to specific structural features.

Defensin-related peptide 1 (Defr1) is allelic to Defb8 and chemoattracts immature DC and CD4+ T cells independently of CCR6

Beta-defensins comprise a family of cationic, antimicrobial and chemoattractant peptides. The six cysteine canonical motif is retained throughout evolution and the disulphide connectivities stabilise the conserved monomer structure. A murine beta-defensin gene (Defr1) present in the main defensin cluster of C57B1/6 mice, encodes a peptide with only five of the canonical six cysteine residues. In other inbred strains of mice, the allele encodes Defb8, which has the six cysteine motif. We show here that in common with six cysteine beta-defensins, defensin-related peptide 1 (Defr1) displays chemoattractant activity for CD4(+) T cells and immature DC (iDC), but not mature DC cells or neutrophils. Murine Defb2 replicates this pattern of attraction. Defb8 is also able to attract iDC but not mature DC. Synthetic analogues of Defr1 with the six cysteines restored (Defr1 Y5C) or with only a single cysteine (Defr1-1c(V)) chemoattract CD4(+) T cells with reduced activity, but do not chemoattract DC. Beta-defensins have previously been shown to attract iDC through CC receptor 6 (CCR6) but neither Defr1 or its related peptides nor Defb8, chemoattract cells overexpressing CCR6. Thus, we demonstrate that the canonical six cysteines of beta-defensins are not required for the chemoattractant activity of Defr1 and that neither Defr1 nor the six cysteine polymorphic variant allele Defb8, act through CCR6.

Preparation of isotopically labelled recombinant beta-defensin for NMR studies

beta-Defensins are a family of cationic peptides that contain six invariant cysteine residues that form characteristic disulfide bonds between Cys(1)-Cys(5), Cys(2)-Cys(4) and Cys(3)-Cys(6). They have been shown to act as potent antimicrobial agents and chemokines. Human beta-defensin 2 (HBD2) was first isolated from psoriatic skin lesions and the structure of this peptide has been solved by X-ray crystallography and NMR spectroscopy both of which are consistent with a fold that contains an N-terminal alpha-helix and three antiparallel beta-strands. Here, we report the expression and purification of the first isotopically labelled beta-defensin ((15)N HBD2) with 100% incorporation of (15)N using a recombinant Escherichia coli method. Multidimensional NMR spectroscopy experiments: 2D (1)H-(15)N HSQC, 3D HSQC-TOCSY and 3D HSQC-NOESY allows for the assignment of resonances with no overlapping or ambiguous peaks. This isotopically labelled peptide is highly suitable for studying the interactions between HBD2 and a range of components from both the mammalian immune system and bacterial pathogens.

Expression of Pla2g2a prevents carcinogenesis in Muc2-deficient mice

Goblet cell depletion and down-regulation of MUC2 expression are observed in a significant percentage of human non-mucinous colorectal adenocarcinomas. Direct evidence for the role of MUC2 in gastrointestinal tumor formation was demonstrated by a knockout of Muc2 in mice that resulted in the development of adenocarcinomas in the small and large intestine. The secretory phospholipase Pla2g2a is a protein that confers resistance to Apc(Min/+)-induced intestinal tumorigenesis. Like Muc2, in the large intestine Pla2g2a is exclusively expressed by the goblet cells and Pla2g2a's tumor resistance is also strongest in the large intestine. Possible genetic interactions between Muc2 and Pla2g2a were examined by creating C57BL/6-Muc2(-/-)Pla2g2a transgenic mice. Expression of a Pla2g2a transgene reduced tumorigenesis in the large intestine by 90% in male Muc2(-/-) mice and by nearly 100% in female Muc2(-/-) mice. Expression of Pla2g2a also inhibited tumor progression. Microarray gene expression studies revealed Pla2g2a target genes that modulate intestinal energy metabolism, differentiation, inflammation, immune responses and proliferation. Overall, results of the present study demonstrate an Apc-independent role for Pla2g2a in tumor resistance and indicate that Pla2g2a plays an important role, along with Muc2, in protection of the intestinal mucosa.

Statistical analysis of interface similarity in crystals of homologous proteins

Many proteins function as homo-oligomers and are regulated via their oligomeric state. For some proteins, the stoichiometry of homo-oligomeric states under various conditions has been studied using gel filtration or analytical ultracentrifugation experiments. The interfaces involved in these assemblies may be identified using cross-linking and mass spectrometry, solution-state NMR, and other experiments. However, for most proteins, the actual interfaces that are involved in oligomerization are inferred from X-ray crystallographic structures using assumptions about interface surface areas and physical properties. Examination of interfaces across different Protein Data Bank (PDB) entries in a protein family reveals several important features. First, similarities in space group, asymmetric unit size, and cell dimensions and angles (within 1%) do not guarantee that two crystals are actually the same crystal form, containing similar relative orientations and interactions within the crystal. Conversely, two crystals in different space groups may be quite similar in terms of all the interfaces within each crystal. Second, NMR structures and an existing benchmark of PDB crystallographic entries consisting of 126 dimers as well as larger structures and 132 monomers were used to determine whether the existence or lack of common interfaces across multiple crystal forms can be used to predict whether a protein is an oligomer or not. Monomeric proteins tend to have common interfaces across only a minority of crystal forms, whereas higher-order structures exhibit common interfaces across a majority of available crystal forms. The data can be used to estimate the probability that an interface is biological if two or more crystal forms are available. Finally, the Protein Interfaces, Surfaces, and Assemblies (PISA) database available from the European Bioinformatics Institute is more consistent in identifying interfaces observed in many crystal forms compared with the PDB and the European Bioinformatics Institute's Protein Quaternary Server (PQS). The PDB, in particular, is missing highly likely biological interfaces in its biological unit files for about 10% of PDB entries.

Directional and balancing selection in human beta-defensins

Background

In primates, infection is an important force driving gene evolution, and this is reflected in the importance of infectious disease in human morbidity today. The beta-defensins are key components of the innate immune system, with antimicrobial and cell signalling roles, but also reproductive functions. Here we examine evolution of beta-defensins in catarrhine primates and variation within different human populations.

Results

We show that five beta-defensin genes that do not show copy number variation in humans show evidence of positive selection in catarrhine primates, and identify specific codons that have been under selective pressure. Direct haplotyping of DEFB127 in humans suggests long-term balancing selection: there are two highly diverged haplotype clades carrying different variants of a codon that, in primates, is positively selected. For DEFB132, we show that extensive diversity, including a four-state amino acid polymorphism (valine, isoleucine, alanine and threonine at position 93), is present in hunter-gatherer populations, both African and non-African, but not found in samples from agricultural populations.

Conclusion

Some, but not all, beta-defensin genes show positive selection in catarrhine primates. There is suggestive evidence of different selective pressures on these genes in humans, but the nature of the selective pressure remains unclear and is likely to differ between populations.

Structure-activity relationships in beta-defensin peptides

The beta-defensins comprise a large family of small cationic antimicrobial peptides widely distributed in plants, mammals and insects. These cysteine rich peptides display multifunctional properties with implications as potential therapeutic agents. Recent research has highlighted their role in both the innate and adaptive immune systems as well as being novel melanocortin ligands. Studies investigating structure and function provide an insight into the molecular basis of their immunological properties.

Interaction of antibacterial peptides spanning the carboxy-terminal region of human beta-defensins 1-3 with phospholipids at the air-water interface and inner membrane of E. coli

Synthetic peptides Phd1-3 spanning the cationic carboxy-terminal region of human beta-defensins HBD-1-3 have been shown to have antibacterial activity. Gross morphological changes were seen in E. coli cells treated with these peptides. In this paper, we have studied the surface-active properties of peptides Phd1-3 and their interactions with different phospholipids using Langmuir-Blodgett monolayers. Compression isotherms and increase in pressure on insertion of peptides into lipid monolayers at different initial pressures indicate the affinity of these peptides for negatively charged lipids. Phd3 inserted less effectively into monolayers as compared to Phd1 and Phd2. The peptides differed in their ability to permeabilize the inner membrane of E. coli, with Phd3 being least effective. It is likely that the peptides kill Gram-negative bacteria by more than one mechanism. When hydrophobicity and net charge favor insertion into lipid membranes, then membrane permeabilization could be the primary event in the killing of bacteria. In cases where membrane insertion does not occur, interaction with phospholipid interface induces highly selective stress that leads to stasis and cell death, as proposed for polymyxin B and bactenecin.

Defensins: Antimicrobial peptides for therapeutic development

A novel class of endogenous antimicrobial peptides called defensins has shown great versatility in their activity against a diverse range of microorganisms including bacteria, viruses and fungi. Their mode of action of bacterial cell lysis seems largely nonspecific and so promises to avert the development of resistance. These two features have made them an area of intense research activity and growing commercial interest. A successful multidisciplinary effort to investigate and develop novel defensins analogues has been established in Singapore that involves computer modeling, biochemistry, proteomics, chemical synthesis, molecular biology and clinical sciences.

A peptide derived from human bactericidal/permeability-increasing protein (BPI) exerts bactericidal activity against Gram-negative bacterial isolates obtained from clinical cases of bovine mastitis

Gram-negative bacteria are responsible for approximately one-third of the clinical cases of bovine mastitis and can elicit a life-threatening, systemic inflammatory response. Lipopolysaccharide (LPS) is a membrane component of Gram-negative bacteria and is largely responsible for evoking the inflammatory response. Antibiotic and anti-inflammatory therapy for treating Gram-negative infections remains suboptimal. Bactericidal/permeability-increasing protein (BPI) is a neutrophil-derived protein with antimicrobial and LPS-neutralizing properties. Select peptide derivatives of BPI are reported to retain these properties. The objective of this study was to evaluate the antimicrobial activity of a human BPI-derived synthetic peptide against clinical bovine mastitis isolates of Gram-negative bacteria. A hybrid peptide was synthesized corresponding to two regions of human BPI (amino acids 90-99 and 148-161), the former of which has bactericidal activity and the latter of which has LPS-neutralizing activity. The minimum inhibitory (MIC) and bactericidal (MBC) concentrations of this peptide against various genera of bacteria were determined using a broth microdilution assay. The MIC's were determined to be: 16-64 microg/ml against Escherichia coli; 32-128 microg/ml against Klebsiella pneumoniae and Enterobacter spp.; and 64-256 microg/ml against Pseudomonas aeruginosa. The MBC's were equivalent to or 1-fold greater than corresponding MIC's. The peptide had no growth inhibitory effect on Serratia marcescens. The antimicrobial activity of the peptide was retained in the presence of serum, but severely impaired in milk. Further functional evaluation of the peptide demonstrated its ability to completely neutralize LPS. Together, these data support additional investigations into the therapeutic application of BPI to the treatment of Gram-negative infections in cattle.