Interaction of indolicidin, a 13-residue peptide rich in tryptophan and proline and its analogues with model membranes

Indolicidin is a 13-residue broad-spectrum antibacterial peptide isolated from bovine neutrophils. The primary structure of the peptide ILPWKWPWWPWRR-amide (IL) reveals an unusually high percentage of tryptophan residues. IL and its analogues where proline residues have been replaced by alanine (ILA) and trp replaced by phe (ILF) show comparable antibacterial activitieso While IL and ILA are haemolytic, ILF does not have this property. Since aromatic residues would strongly favour partitioning of the peptide into the lipid bilayer interface, the biological activities of IL and its analogues could conceivably arise due perturbation of the lipid bilayer of membranes. We have therefore investigated the interaction of IL and its analogues with lipid vesicles. Peptides IL and ILA bind to lipid vesicles composed of phosphatidylcholine and phosphatidylethanol amine: phosphatidyl glycerol: cardiolipin. The position of λmax and I- quenching experiments suggest that the trp residues are localized at the membrane interface and not associated with the hydrophobic core of the lipid bilayer in both the peptides. Hence, membrane permeabilization is likely to occur due to deformation of the membrane surface rather than formation of transmembrane channels by indolicidin and its analogues. Peptides ILA, IL and ILF cause the release of entrapped carboxyfluorescein from phosphatidyl choline vesicles. The peptide-lipid ratios indicate that ILF is less effective than IL and ILA in permeabilizing lipid vesicles, correlating with their haemolytic activities

Potent Adjuvantic Activity of a CCR1-agonistic Bis-Quinoline

A bis-quinoline compound, (7-chloro-N-(4-(7-chloroquinolin-4-ylamino)butyl)quinolin-4-amine; RE-660) was found to have C-C chemokine receptor type 1 (CCR1)-agonistic properties.RE-660 displayed strong adjuvantic activity in mice when co-administered with bovine α-lactalbumin used as a model subunit protein antigen. RE-660 evoked a balanced Th1 (IgG2)/Th2 (IgG1) antibody profile, and the quality of antibodies elicited by the bis-quinoline was found to be superior to that evoked by glucopyranosyl lipid A by surface plasmon resonance experiments. No evidence of proinflammatory activity was observed in human blood ex vivo models. In preliminary acute toxicity studies, the compound was found to be of lower toxicity than chloroquine in mice, and was non-mutagenic in an Ames screen

Structure-Activity Relationships in Toll-like Receptor 2-Agonists Leading to Simplified Monoacyl Lipopeptides

Toll-like receptor 2-agonistic lipopeptides typified by S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-R-cysteinyl-S-serine (PAM2CS) compounds are potential vaccine adjuvants. In continuation of previously reported structure-activity relationships on this chemotype, we have determined that at least one acyl group of optimal length (C16) and an appropriately orientated ester carbonyl group is essential for TLR2-agonistic activity. The spacing between one of the palmitoyl ester carbonyl and the thioether is crucial to allow for an important H-bond, which observed in the crystal structure of the lipopeptide:TLR2 complex; consequently, activity is lost in homologated compounds. Penicillamine-derived analogues are also inactive, likely due to unfavorable steric interactions with the carbonyl of Ser 12 in TLR2. The thioether in this chemotype can be replaced with a selenoether. Importantly, the thioglycerol motif can be dispensed with altogether, and can be replaced with a thioethanol bridge. These results have led to a structurally simpler, synthetically more accessible, and water-soluble analogue possessing strong TLR2-agonistic activities in human blood

The potential for immunoglobulins and host defense peptides (HDPs) to reduce the use of antibiotics in animal production

Abstract Innate defense mechanisms are aimed at quickly containing and removing infectious microorganisms and involve local stromal and immune cell activation, neutrophil recruitment and activation and the induction of host defense peptides (defensins and cathelicidins), acute phase proteins and complement activation. As an alternative to antibiotics, innate immune mechanisms are highly relevant as they offer rapid general ways to, at least partially, protect against infections and enable the build-up of a sufficient adaptive immune response. This review describes two classes of promising alternatives to antibiotics based on components of the innate host defense. First we describe immunoglobulins applied to mimic the way in which they work in the newborn as locally acting broadly active defense molecules enforcing innate immunity barriers. Secondly, the potential of host defense peptides with different modes of action, used directly, induced in situ or used as vaccine adjuvants is described

Prediction of Antibacterial Activity from Physicochemical Properties of Antimicrobial Peptides

Consensus is gathering that antimicrobial peptides that exert their antibacterial action at the membrane level must reach a local concentration threshold to become active. Studies of peptide interaction with model membranes do identify such disruptive thresholds but demonstrations of the possible correlation of these with the in vivo onset of activity have only recently been proposed. In addition, such thresholds observed in model membranes occur at local peptide concentrations close to full membrane coverage. In this work we fully develop an interaction model of antimicrobial peptides with biological membranes; by exploring the consequences of the underlying partition formalism we arrive at a relationship that provides antibacterial activity prediction from two biophysical parameters: the affinity of the peptide to the membrane and the critical bound peptide to lipid ratio. A straightforward and robust method to implement this relationship, with potential application to high-throughput screening approaches, is presented and tested. In addition, disruptive thresholds in model membranes and the onset of antibacterial peptide activity are shown to occur over the same range of locally bound peptide concentrations (10 to 100 mM), which conciliates the two types of observations

Plant bioelectric potential variation in croton (euphorbiaceous genus codiaeum) under natural light conditions pulse anodic stripping voltammetry

Plant bioelectric potential (BEPI variation was observed in actively photosynthesizing leaves of croton plant under natural light conditions. It was found to vary with the intensity of light. BEP reached a 'saturation' value in 4 to 4% hours time on upper surface of leaf, whereas 'saturation' occurred in 2 % hours for the lower surface of the leaf. The BEP of leaf exposed to sunlight was considerably higher than that of leaf covered. The BEP slowly declined after the 'saturation' value during midday and reached a minimum at midnight and early hours of the day. It is suggested here that BEP arises due to light dependent processes namely photosynthesis in plant

Fluorescence and UV resonance Raman study of peptide-vesicle interactions of human cathelicidin LL-37 and its F6W and F17W mutants.

LL-37 is a broad-spectrum human antimicrobial peptide in the cathelicidin family. Potency assays in the form of minimal inhibitory concentration and vesicle leakage indicate that the single-tryptophan mutants, F6W and F17W, are as effective at killing bacteria and disrupting membranes as the native, tryptophan-free LL-37 peptide. Steady-state fluorescence and UV resonance Raman spectroscopy of F6W and F17W reveal molecular details of these tryptophan residues. The local environment polarity, hydrogen bond strength of the indole N-H moiety, and rotational freedom decrease for both F6W and F17W in the presence of carbonate ions relative to in pure distilled water; these results are consistent with burial of the hydrophobic region of alpha-helical LL-37 in oligomeric cores induced in the presence of carbonate ions. Differences in the spectroscopic properties of the carbonate-induced alpha-helical forms of F6W and F17W reflect the presence of a local lysine residue near F6W that makes the microenvironment of F6W more polar than that of F17W. In the presence of lipid vesicles, the mutants undergo additional loss of environment polarity, hydrogen bond strength, and rotational freedom. Quenching experiments utilizing brominated lipids reveal that the tryptophan residues in both mutants are essentially equidistant from the bilayer center and that bromines closer to the bilayer center, in the 9,10 positions, quench fluorescence more efficiently than those closer to the headgroups (6,7 positions). These results support carpeting or toroidal pore mechanisms of membrane disruption by LL-37 and demonstrate that the combination of tryptophan mutants and sensitive spectroscopic tools may provide important molecular clues about antimicrobial action