Human α-defensin 6 promotes mucosal innate immunity through self-assembled peptide nanonets.

Defensins are antimicrobial peptides that contribute broadly to innate immunity, including protection of mucosal tissues. Human α-defensin (HD) 6 is highly expressed by secretory Paneth cells of the small intestine. However, in contrast to the other defensins, it lacks appreciable bactericidal activity.

θ-Defensins: cyclic peptides with endless potential.

θ-Defensins, the only cyclic peptides of animal origin, have been isolated from the leukocytes of rhesus macaques and baboons. Their biogenesis is unusual because each peptide is an 18-residue chimera formed by the head-to-tail splicing of nonapeptides derived from two separate precursors. θ-Defensins have multiple arginines and a ladder-like tridisulfide array spanning their two antiparallel β-strands.

Hapivirins and diprovirins: novel θ-defensin analogs with potent activity against influenza A virus.

θ-Defensins are cyclic octadecapeptides found in nonhuman primates whose broad antiviral spectrum includes HIV-1, HSV-1, severe acute respiratory syndrome coronavirus, and influenza A virus (IAV). We previously reported that synthetic θ-defensins called retrocyclins can neutralize and aggregate various strains of IAV and increase IAV uptake by neutrophils. This study describes two families of peptides, hapivirins and diprovirins, whose design was inspired by retrocyclins.

Sometimes it takes two to tango: contributions of dimerization to functions of human α-defensin HNP1 peptide.

Human myeloid α-defensins called HNPs play multiple roles in innate host defense. The Trp-26 residue of HNP1 was previously shown to contribute importantly to its ability to kill S. aureus, inhibit anthrax lethal factor (LF), bind gp120 of HIV-1, dimerize, and undergo further self-association.

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.

Inerolysin, a cholesterol-dependent cytolysin produced by Lactobacillus iners.

Lactobacillus iners is a common constituent of the human vaginal microbiota. This species was only recently characterized due to its fastidious growth requirements and has been hypothesized to play a role in the pathogenesis of bacterial vaginosis. Here we present the identification and molecular characterization of a protein toxin produced by L.

Defensins enable macrophages to inhibit the intracellular proliferation of Listeria monocytogenes.

Listeria monocytogenes is a facultative intracellular pathogen that infects a large diversity of host cells, including macrophages. To avoid the phagosome microbicidal environment, L. monocytogenes secretes a pore-forming toxin (listeriolysin O, LLO) that releases the bacterium into the cytoplasm.

The formulated microbicide RC-101 was safe and antivirally active following intravaginal application in pigtailed macaques.

Background: RC-101 is a congener of the antiretroviral peptide retrocyclin, which we and others have reported is active against clinical HIV-1 isolates from all major clades, does not hemagglutinate, and is non-toxic and non-inflammatory in cervicovaginal cell culture. Herein, film-formulated RC-101 was assessed for its antiviral activity in vitro, safety in vivo, retention in the cervix and vagina, and ability to remain active against HIV-1 and SHIV after intravaginal application in macaques.

Methodology/principal Findings: RC-101 was formulated as a quick-dissolving film (2000 µg/film), retained complete activity in vitro as compared to unformulated peptide, and was applied intravaginally in six pigtailed macaques daily for four days.

Oxpholipin 11D: an anti-inflammatory peptide that binds cholesterol and oxidized phospholipids.

Background: Many gram-positive bacteria produce pore-forming exotoxins that contain a highly conserved, 12-residue domain (ECTGLAWEWWRT) that binds cholesterol. This domain is usually flanked N-terminally by arginine and C-terminally by valine. We used this 14-residue sequence as a template to create a small library of peptides that bind cholesterol and other lipids.

Trp-26 imparts functional versatility to human alpha-defensin HNP1.

We performed a comprehensive alanine scan of human alpha-defensin HNP1 and tested the ability of the resulting analogs to kill Staphylococcus aureus, inhibit anthrax lethal factor, and bind human immunodeficiency virus-1 gp120. By far, the most deleterious mutation for all of these functions was W26A. The activities lost by W26A-HNP1 were restored progressively by replacing W26 with non-coded, straight-chain aliphatic amino acids of increasing chain length.

De novo sequencing of two new cyclic theta-defensins from baboon (Papio hamadryas) leukocytes by matrix-assisted laser desorption/ionization mass spectrometry.

Two cyclic theta-defensin peptides were isolated from leukocytes of the hamadryas baboon, Papio hamadryas, and purified to homogeneity by gel electrophoresis and reversed-phase high-performance liquid chromatography. Both peptides had high in vitro activity against Escherichia coli, Listeria monocytogenes, methicillin-resistant Staphylococcus aureus (MRSA) and Candida albicans. Here, we report their de novo sequencing by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF-MS).

Antimicrobial mechanism of pore-forming protegrin peptides: 100 pores to kill E. coli.

Antimicrobial peptides (AMPs), important effector molecules of the innate immune system, also provide templates for designing novel antibiotics. Protegrin, an especially potent AMP found in porcine leukocytes, was recently shown to form octameric transmembrane pores. We have employed a combination of experiments and models spanning length scales from the atomistic to the cellular level in order to elucidate the microbicidal mechanism of protegrin.

Through the looking glass, mechanistic insights from enantiomeric human defensins.

Despite the small size and conserved tertiary structure of defensins, little is known at a molecular level about the basis of their functional versatility. For insight into the mechanism(s) of defensin function, we prepared enantiomeric pairs of four human defensins, HNP1, HNP4, HD5, and HBD2, and studied their killing of bacteria, inhibition of anthrax lethal factor, and binding to HIV-1 gp120. Unstructured HNP1, HD5, and HBD3 and several other human alpha- and beta-defensins were also examined.

Antimicrobial host defense peptides in an arteriviral infection: differential peptide expression and virus inactivation.

Antimicrobial host defense peptides (AHDPs) are effective against a wide range of microbes, including viruses. The arteriviral infection caused by porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating pandemic that causes the most economically significant disease of swine. We sought to determine if the expression of AHDPs was influenced by infection with PRRSV, and if porcine AHDPs have direct antiviral activity against PRRSV.

Human alpha-defensins inhibit hemolysis mediated by cholesterol-dependent cytolysins.

Many pathogenic gram-positive bacteria release exotoxins that belong to the family of cholesterol-dependent cytolysins. Here, we report that human alpha-defensins HNP-1 to HNP-3 acted in a concentration-dependent manner to protect human red blood cells from the lytic effects of three of these exotoxins: anthrolysin O (ALO), listeriolysin O, and pneumolysin. HD-5 was very effective against listeriolysin O but less effective against the other toxins.

Multivalent binding of carbohydrates by the human alpha-defensin, HD5.

Four of the six human alpha-defensins (human neutrophil peptides 1-3 and human alpha-defensin 5; HD5) have a lectin-like ability to bind glycosylated proteins. Using HD5 as a model, we applied surface plasmon resonance techniques to gain insights into this property. HD5 bound natural glycoproteins > neoglycoproteins based on BSA > nonglycosylated BSA >> free sugars.

Interactions of alpha-, beta-, and theta-defensins with influenza A virus and surfactant protein D.

We have reported that the alpha-defensins human neutrophil peptides (HNP)-1 and HNP-2 neutralize and aggregate influenza A virus (IAV) and promote uptake of IAV by neutrophils. These alpha-defensins were also shown to bind to surfactant protein (SP)-D and reduce its antiviral activity. In this study, we examined retrocyclin (RC)1 and RC2, humanized versions of the antiviral theta-defensins found in the leukocytes of certain nonhuman primates.

Reawakening retrocyclins: ancestral human defensins active against HIV-1.

Human alpha and beta defensins contribute substantially to innate immune defenses against microbial and viral infections. Certain nonhuman primates also produce theta-defensins-18 residue cyclic peptides that act as HIV-1 entry inhibitors. Multiple human theta-defensin genes exist, but they harbor a premature termination codon that blocks translation.

A novel method for oral delivery of apolipoprotein mimetic peptides synthesized from all L-amino acids.

Administered subcutaneously, D-4F or L-4F are equally efficacious, but only D-4F is orally efficacious because of digestion of L-4F by gut proteases. Orally administering niclosamide (a chlorinated salicylanilide used as a molluscicide, antihelminthic, and lampricide) in temporal proximity to oral L-4F (but not niclosamide alone) in apoE null mice resulted in significant improvement (P < 0.001) in the HDL-inflammatory index (HII), which measures the ability of HDL to inhibit LDL-induced monocyte chemotactic activity in endothelial cell cultures.

Induction of group A Streptococcus virulence by a human antimicrobial peptide.

Group A streptococci (Streptococcus pyogenes or GAS) freshly isolated from individuals with streptococcal sore throat or invasive ("flesh-eating") infection often grow as mucoid colonies on primary culture but lose this colony appearance after laboratory passage. The mucoid phenotype is due to abundant production of the hyaluronic acid capsular polysaccharide, a key virulence determinant associated with severe GAS infections. These observations suggest that signal(s) from the human host trigger increased production of capsule and perhaps other virulence factors during infection.

Anti-inflammatory apoA-I-mimetic peptides bind oxidized lipids with much higher affinity than human apoA-I.

4F is an anti-inflammatory, apolipoprotein A-I (apoA-I)-mimetic peptide that is active in vivo at nanomolar concentrations in the presence of a large molar excess of apoA-I. Physiologic concentrations ( approximately 35 microM) of human apoA-I did not inhibit the production of LDL-induced monocyte chemotactic activity by human aortic endothelial cell cultures, but adding nanomolar concentrations of 4F in the presence of approximately 35 microM apoA-I significantly reduced this inflammatory response. We analyzed lipid binding by surface plasmon resonance.

Correlation between simulated physicochemical properties and hemolycity of protegrin-like antimicrobial peptides: predicting experimental toxicity.

The therapeutic, antibiotic potential of antimicrobial peptides can be prohibitively diminished because of the cytotoxicity and hemolytic profiles they exhibit. Quantifying and predicting antimicrobial peptide toxicity against host cells is thus an important goal of AMP related research. In this work, we present quantitative structure activity relationships for toxicity of protegrin-like antimicrobial peptides against human cells (epithelial and red blood cells) based on physicochemical properties, such as interaction energies and radius of gyration, calculated from molecular dynamics simulations of the peptides in aqueous solvent.