Antimicrobial peptides

About: Antimicrobial peptides is a research topic. Over the lifetime, 10645 publications have been published within this topic receiving 507688 citations. The topic is also known as: host defense peptide & antimicrobial protein.

APD: the Antimicrobial Peptide Database

Abstract: An antimicrobial peptide database (APD) has been established based on an extensive literature search. It contains detailed information for 525 peptides (498 antibacterial, 155 antifungal, 28 antiviral and 18 antitumor). APD provides interactive interfaces for peptide query, prediction and design. It also provides statistical data for a select group of or all the peptides in the database. Peptide information can be searched using keywords such as peptide name, ID, length, net charge, hydrophobic percentage, key residue, unique sequence motif, structure and activity. APD is a useful tool for studying the structure-function relationship of antimicrobial peptides. The database can be accessed via a web-based browser at the URL: http://aps.unmc.edu/AP/main.html.

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.

Plant defensins: novel antimicrobial peptides as components of the host defense system.

Abstract: Various mechanisms to fend off microbial invaders have been devised by all living organisms, including microorganisms themselves. The most sophisticated of these mechanisms relies on the synthesis of immunoglobulins directed against specific microbial targets. However, immunoglobulin-based immunity operates only in a relatively minor subset of living species, namely the higher vertebrates. A much more ancient and widespread defense strategy involves the production of small peptides that exert antimicrobial properties. As products of single genes, antimicrobial peptides can be synthesized in a swift and flexible way, and because of their small size they can be produced by the host with a minimal input of energy and biomass. Wellknown examples of antimicrobial peptides are the cecropins that accumulate in the hemolymph of many invertebrates in response to injury or infection (reviewed by Boman and Hultmark, 1987) and the magainins that are secreted by glands in the skin of amphibians (reviewed by Bevins and Zasloff, 1990). Cecropins and magainins are small (20-40 residues) basic peptides displaying an amphipathic a-helical structure that can integrate in microbial membranes to form ion channels (Duclohier, 1994). Another class of antimicrobial peptides is formed by the Cys-rich peptides, which in contrast to cecropins and magainins, have a complex cystine-stabilized three-dimensional folding pattern often involving antiparallel ,3-sheets. Defensins are one class among the numerous types of Cys-rich antimicrobial peptides, which differ in length, number of cystine, bonds, or folding pattern (reviewed by Boman, 1995). Insect defensins (34-43 residues, three disulfide bridges) are, like cecropins, produced in a pathogeninducible manner by the insect fat body and secreted in the hemolymph (reviewed by Hoffmann and Hetru, 1992). Mammalian defensins (29-34 amino acids, three disulfide bridges) are produced by various specialized cells in the mammalian body (reviewed by Lehrer et al., 1993; Ganz and Lehrer, 1994). For example, they are very abundant in granules of phagocytic blood cells. These granules fuse with phagocytosis vesicles containing microorganisms, where the defensins are thought to contribute, together with other antimicrobial proteins and active oxygen species, to killing of the engulfed microorganisms. Defensins are also secreted by epithelial cells of the intestines and airways, where they may help maintain the normal microbial flora in a steady state. In addition, the expression of defensins in the airway epithelium has been shown to be up-regulated after exposure to bacterial lipopolysaccharides (Diamond et al., 1993). The importance of defensins in innate immunity of humans is underscored by the observation that certain disorders characterized by recurrent infections are associated with a lack of defensins in blood phagocytes (Ganz et al., 1988). Moreover, transposon mutants of a pathogenic Salmonella strain known to infect and grow inside phagocytes simultaneously lost their resistance to defensins (and other antimicrobial peptides) and their virulence (Groisman et al., 1992). Recently, we characterized a novel class of plant peptides whose structural and functional properties resemble those of insect and mammalian defensins. Hence, we termed this family of peptides "plant defensins" (Terras et al., 1995).

Amyloid-β peptide protects against microbial infection in mouse and worm models of Alzheimer’s disease

Abstract: The amyloid-β peptide (Aβ) is a key protein in Alzheimer’s disease (AD) pathology. We previously reported in vitro evidence suggesting that Aβ is an antimicrobial peptide. We present in vivo data showing that Aβ expression protects against fungal and bacterial infections in mouse, nematode, and cell culture models of AD. We show that Aβ oligomerization, a behavior traditionally viewed as intrinsically pathological, may be necessary for the antimicrobial activities of the peptide. Collectively, our data are consistent with a model in which soluble Aβ oligomers first bind to microbial cell wall carbohydrates via a heparin-binding domain. Developing protofibrils inhibited pathogen adhesion to host cells. Propagating β-amyloid fibrils mediate agglutination and eventual entrapment of unatttached microbes. Consistent with our model, Salmonella Typhimurium bacterial infection of the brains of transgenic 5XFAD mice resulted in rapid seeding and accelerated β-amyloid deposition, which closely colocalized with the invading bacteria. Our findings raise the intriguing possibility that β-amyloid may play a protective role in innate immunity and infectious or sterile inflammatory stimuli may drive amyloidosis. These data suggest a dual protective/damaging role for Aβ, as has been described for other antimicrobial peptides.

Staphylococcus aureus resistance to human defensins and evasion of neutrophil killing via the novel virulence factor MprF is based on modification of membrane lipids with L-lysine

Abstract: Defensins, antimicrobial peptides of the innate immune system, protect human mucosal epithelia and skin against microbial infections and are produced in large amounts by neutrophils. The bacterial pathogen Staphylococcus aureus is insensitive to defensins by virtue of an unknown resistance mechanism. We describe a novel staphylococcal gene, mprF, which determines resistance to several host defense peptides such as defensins and protegrins. An mprF mutant strain was killed considerably faster by human neutrophils and exhibited attenuated virulence in mice, indicating a key role for defensin resistance in the pathogenicity of S. aureus. Analysis of membrane lipids demonstrated that the mprF mutant no longer modifies phosphatidylglycerol with l-lysine. As this unusual modification leads to a reduced negative charge of the membrane surface, MprF-mediated peptide resistance is most likely based on repulsion of the cationic peptides. Accordingly, inactivation of mprF led to increased binding of antimicrobial peptides by the bacteria. MprF has no similarity with genes of known function, but related genes were identified in the genomes of several pathogens including Mycobacterium tuberculosis, Pseudomonas aeruginosa, and Enterococcus faecalis. MprF thus constitutes a novel virulence factor, which may be of general relevance for bacterial pathogens and represents a new target for attacking multidrug resistant bacteria.