Showing papers on "Antimicrobial peptides published in 1997"

A peptide antibiotic from human skin

Abstract: To avoid opportunistic infections, plants and animals have developed antimicrobial peptides in their epithelia that can form pores in the cytoplasmic membrane of microorganisms1. After contact with microorganisms, vertebrate skin2, trachea and tongue epithelia3 are rich sources of peptide antibiotics1, which may explain the unexpected resistance of these tissues to infection. Here we report that human skin is protected in a similar way by an inducible, transcriptionally regulated, antibiotic peptide, which resembles those in other mammals.

Drosophila host defense: Differential induction of antimicrobial peptide genes after infection by various classes of microorganisms

Abstract: Insects respond to microbial infection by the rapid and transient expression of several genes encoding potent antimicrobial peptides. Herein we demonstrate that this antimicrobial response of Drosophila is not aspecific but can discriminate between various classes of microorganisms. We first observe that the genes encoding antibacterial and antifungal peptides are differentially expressed after injection of distinct microorganisms. More strikingly, Drosophila that are naturally infected by entomopathogenic fungi exhibit an adapted response by producing only peptides with antifungal activities. This response is mediated through the selective activation of the Toll pathway.

Quorum sensing by peptide pheromones and two-component signal-transduction systems in Gram-positive bacteria

Abstract: Cell-density-dependent gene expression appears to be widely spread in bacteria. This quorum-sensing phenomenon has been well established in Gram-negative bacteria, where N-acyl homoserine lactones are the diffusible communication molecules that modulate cell-density-dependent phenotypes. Similarly, a variety of processes are known to be regulated in a cell-density- or growth-phase-dependent manner in Gram-positive bacteria. Examples of such quorum-sensing modes in Gram-positive bacteria are the development of genetic competence in Bacillus subtilis and Streptococcus pneumoniae, the virulence response in Staphylococcus aureus, and the production of antimicrobial peptides by several species of Gram-positive bacteria including lactic acid bacteria. Cell-density-dependent regulatory modes in these systems appear to follow a common theme, in which the signal molecule is a post-translationally processed peptide that is secreted by a dedicated ATP-binding-cassette exporter. This secreted peptide pheromone functions as the input signal for a specific sensor component of a two-component signal-transduction system. Moreover, genetic linkage of the common elements involved results in autoregulation of peptide-pheromone production.

Antimicrobial Peptides from Plants

Abstract: Peptides with antimicrobial properties are present in most if not all plant species All plant antimicrobial peptides isolated so far contain even numbers of cysteines (4, 6, or 8), which are all pairwise connected by disulfide bridges, thus providing high stability to the peptides Based on homologies at the primary structure level, plant antimicrobial peptides can be classified into distinct families including thionins, plant defensins, lipid transfer proteins, and he vein- and knottin-type antimicrobial peptides Detailed three-dimensional structure information has been obtained for one or more members of these peptide families All antimicrobial peptides studied thus far appear to exert their antimicrobial effect at the level of the plasma membrane of the target microorganism, but the different peptide types are likely to act via different mechanisms Antimicrobial peptides can occur in all plant organs In unstressed organs, antimicrobial peptides are usually most abundant in the outer cell

Ribosomally synthesized antimicrobial peptides: their function, structure, biogenesis, and mechanism of action

Abstract: Ribosomally synthesized peptides with antimicrobial activity are produced by prokaryotes, plants, and a wide variety of animals, both vertebrates and invertebrates. These peptides represent an important defense against micro-organisms. Although the peptides differ greatly in primary structures, they are nearly all cationic and very often amphiphilic, which reflects the fact that many of these peptides kill their target cells by permeabilizing the cell membrane. Moreover, many of these peptides may roughly be placed into one of three groups: (1) those that have a high content of one (or two) amino acid(s), often proline, (2) those that contain intramolecular disulfide bonds, often stabilizing a predominantly beta-sheet structure, and (3) those with amphiphilic regions if they assume an alpha-helical structure. Most known ribosomally synthesized antimicrobial peptides have been identified and characterized during the past 15 years. As a result of these studies, insight has been gained into fundamental aspects of biology and biochemistry such as innate immunity, membrane-protein interactions, and protein modification and secretion. Moreover, it has become evident that these peptides may be developed into useful antimicrobial additives and drugs. This review presents a broad overview of the main types of ribosomally synthesized antimicrobial peptides produced by eukaryotes and prokaryotes.

Biochemical properties of regulatory peptides derived from milk proteins.

Abstract: Biologically active peptides derived from milk proteins are inactive within the sequence of the precursor proteins but can be released by enzymatic proteolysis. Based on structure-activity studies, peptides with a defined bioactivity show common structural features. Moreover, many milk protein-derived peptides reveal multifunctional bioactivities. Bioactive peptide fragments originating from milk proteins should be taken into account as potential modulators of various regulatory processes in the body. Opioid peptides are opioid receptor ligands with agonistic or antagonistic activities. Angiotensin converting enzyme (ACE) inhibitory peptides can exert an antihypertensive effect. Immunomodulating casein peptides have been found to stimulate the proliferation of human lymphocytes and the phagocytic activities of macrophages. Antimicrobial peptides have been shown to kill sensitive microorganisms. Antithrombotic peptides inhibit the fibrinogen binding to a specific receptor region on the platelet surface and also inhibit aggregation of platelets. Casein phosphopeptides can form soluble organophosphate salts and may function as carriers for different minerals, especially calcium. In relation to their mode of action, bioactive peptides may reach target sites (e.g., receptors, enzymes) at the luminal side of the intestinal tract or after absorption, in peripheral organs. The physiological significance of bioactive peptides as exogenous regulatory substances is not yet fully understood. Nevertheless, several bioactive peptides derived from milk proteins have been shown to exert beneficial physiological effects. Milk-derived peptides were already produced on an industrial scale and as a consequence these peptides have been considered for application both as dietary supplements in "functional foods" and as drugs.

Effects of pH and salinity on the antimicrobial properties of clavanins.

Abstract: Clavanins are histidine-rich, amidated alpha-helical antimicrobial peptides that were originally isolated from the leukocytes (hemocytes) of a tunicate, Styela clava. The activities of clavanin A amide and clavanin A acid against Escherichia coli, Listeria monocytogenes, and Candida albicans were substantially greater at pH 5.5 than at pH 7.4. In contrast, clavanin AK, a synthetic variant of clavanin A acid containing 4 histidine-->lysine substitutions exerted substantial activity at both pH 7.4 and pH 5.5. Each of these three clavanins permeabilized the outer and inner membranes of E. coli very effectively at pH 5.5, but only clavanin AK did so at pH 7.4. Unlike magainin 1 and cecropin P1, alpha-helical antimicrobial peptides from frog skin and porcine intestine, respectively, clavanins were broadly effective against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, as well as gram-negative organisms. Because clavanins exert substantial antimicrobial activity in 0.1 to 0.3 M NaCl, they provide templates for designing broad-spectrum peptide antibiotics intended to function in extracellular environments containing normal or elevated NaCl concentrations. The pH-dependent properties of histidine-rich antimicrobial peptides may allow the design of agents that would function selectively in acidic compartments, such as the gastric lumen, or within phagolysosomes.

Epithelial antibiotic induced in states of disease

Abstract: Epithelial defensins provide an active defense against the external microbial environment. We investigated the distribution and expression of this class of antimicrobial peptides in normal cattle and in animals in varying states of disease. β-defensin mRNA was found to be widely expressed in numerous exposed epithelia but was found at higher levels in tissues that are constantly exposed to and colonized by microorganisms. We observed induction in ileal mucosa during chronic infection with Mycobacterium paratuberculosis and in bronchial epithelium after acute infection with Pasteurella haemolytica. It has been proposed that expression of antimicrobial peptides is an integral component of the inflammatory response. The results reported here support this hypothesis and suggest that epithelial defensins provide a rapidly mobilized local defense against infectious organisms.

D-amino acids in animal peptides.

Abstract: D-amino acids have been detected in a variety of peptides synthesized by animal cells. These include opiate and antimicrobial peptides from amphibian skin, neuropeptides from snail ganglia, a hormone from crustaceans, and a constituent of a spider venom. cDNA cloning has shown that at those positions where a D-amino acid is found in the end-product, a normal codon for the corresponding L-amino acid is present. This implies that the D-residues are formed from L-amino acids by a posttranslational reaction. A prototype enzyme catalyzing such a reaction has recently been isolated from the venom of the funnel web spider.

Synthetic histatin analogues with broad-spectrum antimicrobial activity

Abstract: Histatins are salivary histidine-rich cationic peptides, ranging from 7 to 38 amino acid residues in length, that exert a potent killing effect in vitro on Candida albicans. Starting from the C-terminal fungicidal domain of histatin 5 (residues 11-24, called dh-5) a number of substitution analogues were chemically synthesized to study the effect of amphipathicity of the peptide in helix conformation on candidacidal activity. Single substitutions in dh-5 at several positions did not have any effect on fungicidal activity. However, multi-site substituted analogues (dhvar1 and dhvar2) exhibited a 6-fold increased activity over dh-5. In addition, dhvar1 and dhvar2 inhibited the growth of the second most common yeast found in clinical isolates, Torulopsis glabrata, of oral- and non-oral pathogens such as Prevotella intermedia and Streptococcus mutans, and of a methicillin-resistant Staphylococcus aureus. In their broad-spectrum activity, dhvar1 and dhvar2 were comparable to magainins (PGLa and magainin 2), antimicrobial peptides of amphibian origin. Both the fungicidal and the haemolytic activities of dhvar1, dhvar2 and magainins increased at decreasing ionic strength.

Antimicrobial peptide defense in Drosophila

Abstract: Drosophila responds to a septic injury by the rapid synthesis of antimicrobial peptides. These molecules are predominantly produced by the fat body, a functional equivalent of mammalian liver, and are secreted into the hemolymph where their concentrations can reach up to 100 microM. Six distinct antibacterial peptides (plus isoforms) and one antifungal peptide have been characterized in Drosophila and their genes cloned. The induction of the gene encoding the antifungal peptide relies on the spatzle/Toll/cactus gene cassette, which is involved in the control of dorsoventral patterning in the embryo, and shows interesting structural and functional similarities with cytokine-induced activation of NF-kappa B in mammalian cells. An additional pathway, dependent on the as yet unidentified imd (for immune-deficiency) gene, is required for the full induction of the antibacterial peptide genes. Mutants deficient for the Toll and imd pathways exhibit a severely reduced survival to fungal and bacterial infections, respectively. Recent data on the molecular mechanisms underlying recognition of non-self are also discussed in this review.

Antimicrobial peptides of leukocytes.

Abstract: Leukocytes use an array of antimicrobial peptides and proteins to help them destroy invading microorganisms. These endogenous antibiotic molecules are remarkable for their structural variety, rapid evolutionary divergence, intraspecies variation, and complex yet subtle interactions with their target

Fabatins: new antimicrobial plant peptides

Abstract: Two new antimicrobial peptides related to the γ-thionine family have been isolated by acid extraction from the broad bean Vicia faba. The extract was separated by ion exchange chromatography, and a fraction showing antibacterial activity was further purified by reverse-phase HPLC. Material from a single HPLC peak was sequenced and revealed the presence of two peptides differing by one amino acid. The peptides were named fabatins. They are 47 amino acids long, have an overall positive charge and contain 8 cysteines that probably form 4 disulfide bridges characteristic of the γ-thionins. Fabatins were active against both Gram-negative and Gram-positive bacteria, but were inactive against the yeasts Saccharomyces cerevisiae and Candida albicans.

Porcine polymorphonuclear leukocytes generate extracellular microbicidal activity by elastase-mediated activation of secreted proprotegrins.

Abstract: Antimicrobial peptides of several structural classes have been found in phagocytes and epithelial cells of many animals. The broadly microbicidal protegrins (PG1, -2, and -3) were originally isolated as 16 to 18-amino-acid peptides from pig neutrophil lysates, but the corresponding cDNA sequences encoded much larger precursors that belonged to the cathelicidin family of antimicrobial peptides. We explored the storage, secretion, and microbicidal activation of protegrins in porcine neutrophils and in a model system consisting of recombinant proprotegrin 3 (pPG3) and various serine proteases and their inhibitors. Protegrins were stored in neutrophils as inactive proforms that were cleaved by neutrophil elastase to mature protegrins during the preparation of granule lysate and during phorbol myristate acetate-stimulated granule secretion from intact neutrophils. Recombinant pPG3 was efficiently cleaved by trace amounts of human neutrophil elastase or equivalent amounts of elastase activity from porcine neutrophils, but pPG3 was relatively resistant to porcine pancreatic elastase or human neutrophil cathepsin G. The recombinant pPG3 and neutrophil proprotegrins lacked microbicidal activity, but the mature protegrins generated in the elastase-mediated cleavage reaction were as active against Listeria monocytogenes as the chemically synthesized protegrin. The secretion and elastase-mediated activation of proprotegrins accounted for much of the stable microbicidal activity of porcine neutrophil secretions against L. monocytogenes. Secreted proprotegrins and trace amounts of elastase constitute a binary microbicidal system that is likely to contribute to the antimicrobial activity of porcine inflammatory fluids.

Design of Synthetic Antimicrobial Peptides Based on Sequence Analogy and Amphipathicity

Abstract: Novel alpha-helical antimicrobial peptides have been devised by comparing the N-terminal sequences of many of these peptides from insect, frog and mammalian families, extracting common features, and creating sequence templates with which to design active peptides. Determination of the most frequent amino acids in the first 20 positions for over 80 different natural sequences allowed the design of one peptide, while a further three were based on the comparison of the sequences of alpha-helical antimicrobial peptides derived from the mammalian cathelicidin family of precursors. These peptides were predicted to assume a highly amphipathic alpha-helical conformation, as indicated by high mean hydrophobic moments. In fact, circular dichroism experiments showed clear transitions from random coil in aqueous solution to an alpha-helical conformation on addition of trifluoroethanol. All four peptides displayed a potent antibacterial activity against selected gram-positive and gram-negative bacteria (minimum inhibitory concentrations in the range 1-8 microM), including some antibiotic resistant strains. Permeabilization of both the outer and cytoplasmic membranes of the gram-negative bacterium, Escherichia coli, by selected peptides was quite rapid and a dramatic drop in colony forming units was observed within 5 min in time-killing experiments. Permeabilization of the cytoplasmic membrane of the gram-positive bacterium, Staphylococcus aureus, was instead initially quite slow, gathering speed after 45 min, which corresponds to the time required for significant inactivation in time-killing studies. The cytotoxic activity of the peptides, determined on several normal and transformed cell lines, was generally low at values within the minimum inhibitory concentration range.

Differential scanning microcalorimetry indicates that human defensin, HNP-2, interacts specifically with biomembrane mimetic systems.

Abstract: α-Defensins are antimicrobial peptides with 29−35 amino acid residues and cysteine-stabilized amphiphilic, triple-stranded β-sheet structures. We used high-precision differential scanning microcalo...