Aleksander Patrzykat

Sublethal Concentrations of Pleurocidin-Derived Antimicrobial Peptides Inhibit Macromolecular Synthesis in Escherichia coli

Cationic bactericidal peptides are components of natural host defenses against infections. While the mode of antibacterial action of cationic peptides remains controversial, several targets, including the cytoplasmic membrane and macromolecular synthesis, have been identified for peptides acting at high concentrations. The present study identified peptide effects at lower, near-lethal inhibitory concentrations. An amidated hybrid of the flounder pleurocidin and the frog dermaseptin (P-Der), two other pleurocidin derivatives, and pleurocidin itself were studied. At 2 microg/ml, the MIC, P-Der inhibited Escherichia coli growth in a broth dilution assay but did not cause bacterial death within 30 min, as estimated by viable count analysis. Consistent with this, P-Der demonstrated a weak ability to permeabilize membranes but was able to translocate across the lipid bilayer of unilamellar liposomes. Doses of 20 microg/ml or more reduced bacterial viable counts by about 2 log orders of magnitude within 5 min after peptide treatment. Abrupt loss of cell membrane potential, observed with a fluorescent dye, dipropylthiacarbocyanine, paralleled bacterial death but did not occur at the sublethal, inhibitory concentrations. Both lethal and sublethal concentrations of P-Der affected macromolecular synthesis within 5 min, as demonstrated by incorporation of [3H]thymidine, [3H]uridine, and [3H]histidine, but the effects were qualitatively distinct at the two concentrations. Variations of the inhibition pattern described above were observed for pleurocidin and two other derivatives. Our results indicate that peptides at their lowest inhibitory concentrations may be less capable of damaging cell membranes, while they maintain their ability to inhibit macromolecular synthesis. Better understanding of the effects of peptides acting at their MICs will contribute to the design of new peptides effective at lower, less toxic concentrations.

Structure and Mechanism of Action of an Indolicidin Peptide Derivative with Improved Activity against Gram-positive Bacteria*

Indolicidin, an antimicrobial peptide with a unique amino acid sequence (ILPWKWPWWPWRR-NH2) is found in bovine neutrophils. A derivative of indolicidin, CP10A, has alanine residues substituted for proline residues and has improved activity against Gram-positive organisms. Transmission electron microscopy of Staphylococcus aureus andStaphylococcus epidermidis treated with CP10A showed mesosome-like structures in the cytoplasm. The peptide at 2-fold the minimal inhibitory concentration did not show significant killing ofS. aureus ISP67 (a histidine, uridine, and thymidine auxotroph) but did show an early effect on histidine and uridine incorporation and, later, an effect on thymidine incorporation. Upon interaction with liposomes, detergents, and lipoteichoic acid, CP10A was shown by circular dichroism spectroscopy to undergo a change in secondary structure. Fluorescence spectroscopy indicated that the tryptophan residues were located at the hydrophobic/hydrophilic interface of liposomes and detergent micelles and were inaccessible to the aqueous quencher KI. The three-dimensional structure of CP10A in the lipid mimetic dodecylphosphocholine was determined using two-dimensional NMR methods and was characterized as a short, amphipathic helical structure, whereas indolicidin was previously shown to have an extended structure. These studies have introduced a cationic peptide with a unique structure and an ability to interact with membranes and to affect intracellular synthesis of proteins, RNA, and DNA.

Synergy of Histone-Derived Peptides of Coho Salmon with Lysozyme and Flounder Pleurocidin

ABSTRACT Recent research has identified endogenous cationic antimicrobial peptides as important factors in the innate immunity of many organisms, including fish. It is known that antimicrobial activity, as well as lysozyme activity, can be induced in coho salmon (Oncorhynchus kisutch) mucus after exposure of the fish to infectious agents. Since lysozyme alone does not have antimicrobial activity against Vibrio anguillarum and Aeromonas salmonicida, a four-step protein purification protocol was used to isolate and identify antibacterial fractions from bacterially challenged coho salmon mucus and blood. The purification consisted of extraction with hot acetic acid, extraction and concentration on a C18 cartridge, gel filtration, and reverse-phase chromatography on a C18 column. N-terminal amino acid sequence analyses revealed that both the blood and the mucus antimicrobial fractions demonstrated identity with the N terminus of trout H1 histone. Mass spectroscopic analysis indicated the presence of the entire histone, as well as fragments thereof, including a 26-amino-acid N-terminal segment. These fractions inhibited the growth of antibiotic-supersuscptible Salmonella enterica serovar Typhimurium, as well as A. salmonicida and V. anguillarum. Synthetic peptides identical to the N-terminally acetylated or C-terminally amidated 26-amino-acid fragment were inactive in antimicrobial assays, but they potentiated the antimicrobial activities of the flounder peptide pleurocidin, lysozyme, and crude lysozyme-containing extracts from coho salmon. The peptides bound specifically to anionic lipid monolayers. However, synergy with pleurocidin did not appear to occur at the cell membrane level. The synergistic activities of inducible histone peptides indicate that they play an important role in the first line of salmon defenses against infectious pathogens and that while some histone fragments may have direct antimicrobial effects, others improve existing defenses.

Novel Antimicrobial Peptides Derived from Flatfish Genes

ABSTRACT We report on the identification of active novel antimicrobials determined by screening both the genomic information and the mRNA transcripts from a number of different flatfish for sequences encoding antimicrobial peptides, predicting the sequences of active peptides from the genetic information, producing the predicted peptides chemically, and testing them for their activities. We amplified 35 sequences from various species of flatfish using primers whose sequences are based on conserved flanking regions of a known antimicrobial peptide from winter flounder, pleurocidin. We analyzed the sequences of the amplified products and predicted which sequences were likely to encode functional antimicrobial peptides on the basis of charge, hydrophobicity, relation to flanking sequences, and similarity to known active peptides. Twenty peptides were then produced synthetically and tested for their activities against gram-positive and gram-negative bacteria and the yeast Candida albicans. The most active peptide (with the carboxy-terminus amidated sequence GWRTLLKKAEVKTVGKLALKHYL, derived from American plaice) showed inhibitory activity over a concentration range of 1 to 8 μg/ml against a test panel of pathogens, including the intrinsically antibiotic-resistant organism Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and C. albicans. The methods described here will be useful for the identification of novel peptides with good antimicrobial activities.

Antimicrobial peptides: cooperative approaches to protection.

Reports of cationic antimicrobial peptides (CAPs) have become standard fare in research literature. But with several hundred peptides described to date, the investigator who tries to navigate the proposed models of their activity is only treated to a generous serving of incongruencies. Rather than acting in isolation as antimicrobial molecules, CAPs also may synergize with other molecules of innate immunity and modulate both innate and adaptive immune systems, thus providing a link between the various mechanisms that result in host protection.