Antimicrobial peptides (AMPs) are important components of the innate immune system of animals, plants, fungi and bacteria and are recently under discussion as promising alternatives to conventional antibiotics. We have investigated two cecropin-like synthetic peptides, Gm1, which corresponds to the natural overall uncharged Galleria mellonella native peptide and ?Gm1, a modified overall positively charged Gm1 variant. We have analysed these peptides for their potential to inhibit the endotoxin-induced secretion of tumour necrosis factor-? (TNF-?) from human mononuclear cells. Furthermore, in a conventional microbiological assay, the ability of these peptides to inhibit the growth of the rough mutant bacteria Salmonella enterica Minnesota R60 and the polymyxin B-resistant Proteus mirabilis R45 was investigated and atomic force microscopy (AFM) measurements were performed to characterize the morphology of the bacteria treated by the two peptides. We have also studied their cytotoxic properties in a haemolysis assay to clarify potential toxic effects. Our data revealed for both peptides minor anti-inflammatory (anti-endotoxin) activity, but demonstrated antimicrobial activity with differences depending on the endotoxin composition of the respective bacteria. In accordance with the antimicrobial assay, AFM data revealed a stronger morphology change of the R45 bacteria than for the R60. Furthermore, Gm1 had a stronger effect on the bacteria than ?Gm1, leading to a different morphology regarding indentations and coalescing of bacterial structures. The findings verify the biophysical measurements with the peptides on model systems. Both peptides lack any haemolytic activity up to an amount of 100?g/ml, making them suitable as new anti-infective agents.
Natural occurring antimicrobial peptides (AMPs) are important components of the innate immune system of animals and plants. They are considered to be promising alternatives to conventional antibiotics. Here we present a comparative study of two synthetic peptides: Gm1, corresponding to the natural overall uncharged peptide from Galleria mellonella (Gm) and ?Gm1, a modified overall positively charged Gm1 variant. We have studied the interaction of the peptides with lipid membranes composed of different kinds of lipopolysaccharides (LPS) and dimyristoylphosphatidylglycerol (DMPG), in some cases also dimyristoylphosphatidylethanolamine (DMPE) as representative lipid components of Gram-negative bacterial membranes, by applying Fourier-transform infrared spectroscopy (FTIR), Förster resonance energy transfer spectroscopy (FRET), differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC). Gm1 generates a destabilizing effect on the gel to liquid crystalline phase transition of the acyl chains of the lipids, as deduced from a decrease in the phase transition temperature and enthalpy, suggesting a fluidization, whereas ?Gm1 led to the opposite behavior. Further, FTIR analysis of the functional groups of the lipids participating in the interaction with the peptides indicated a shift in the band position and intensity of the asymmetric PO2(-) stretching vibration originating from the lipid phosphate groups, a consequence of the sterical changes in the head group region. Interestingly, FRET spectroscopy showed a similar intercalation of both peptides into the DMPG and LPS, but much less into the DMPE membrane systems. These results are discussed in the light of a possible use of the peptides as antimicrobial and anti-endotoxin drugs.
Interleukin-5 (IL-5) is the key mediator for the function of eosinophil granulocytes, whose deregulation is characteristic of hypereosinophilic diseases and presumably contributes to allergic asthma. IL-5 signaling involves two transmembrane receptors, IL-5R? and the common ? chain, which upon formation of the ternary complex activate the JAK/STAT signaling cascade. To investigate the mechanism underlying ligand-receptor recognition, we determined the structure of IL-5 bound to the extracellular domain of IL-5R?. IL-5 makes contact with all three fibronectin III-like domains of IL-5R?, with the receptor architecture resembling a wrench. Mutagenesis data provide evidence that this wrench-like architecture is likely preformed. The structure demonstrates that for steric reasons, homodimeric IL-5 can bind only one receptor molecule, even though two equivalent receptor-binding sites exist. In regard to strong efforts being made to develop IL-5 antagonists for treating asthma and hypereosinophilic diseases, the advances in molecular understanding provided by this structure are of greatest value.
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