Importance of Tryptophan in Transforming an Amphipathic Peptide into a Pseudomonas aeruginosa-Targeted Antimicrobial Peptide.

Here, we found that simple substitution of amino acids in the middle position of the hydrophobic face of an amphipathic peptide RI16 with tryptophan (T9W) considerably transformed into an antimicrobial peptide specifically targeting Pseudomonas aeruginosa. Minimal inhibitory concentration (MIC) results demonstrated that T9W had a strong and specifically antimicrobial activity against P. aeruginosa, including antibiotic-resistant strains, but was not active against Escherichia coli, Salmonella typhimurium, Staphylococcus aureus and Staphyfococcus epidermidis. Fluorescent spectroscopic assays indicated that T9W interacted with the membrane of P. aeruginosa, depolarizing the outer and the inner membrane of bacterial cells. Salt susceptibility assay showed that T9W still maintained its strong anti-pseudomonas activity in the presence of salts at physiological concentrations, and in hemolytic and MTT assays T9W also showed no toxicity against human blood cells and macrophages. In vivo assay demonstrated that T9W also displayed no toxicity to Chinese Kun Ming (KM) mice. Furthermore, the strong antibiofilm activity was also observed with the peptide T9W, which decreased the percentage of biomass formation in a dose-dependent manner. Overall, these findings indicated that design of single-pathogen antimicrobial agents can be achieved by simple amino acid mutation in naturally occurring peptide sequences and this study suggested a model of optimization/design of anti-pseudomonas drugs in which the tryptophan residue was a conserved element

Key physicochemical parameters of parental and mutant peptides.

<p>Key physicochemical parameters of parental and mutant peptides.</p

Helical wheel projections of the peptides.

<p>By default the output presents the hydrophilic residues as circles, hydrophobic residues as diamonds, potentially negatively charged as triangles and potentially positively charges as pentagons. Hydrophobicity is color coded as well: the most hydrophobic reside is green, and the amount of green decreases proportionally to the hydrophobicity, with zero hydrpphobicity coded as yellow. The positively charged residues are grey and the hydrophilic residues are coded orange. The wheel projection was performed online using the Helical Wheel Projections: <a href="http://rzlab.ucr.edu/scripts/wheel/wheel.cgi" target="_blank">http://rzlab.ucr.edu/scripts/wheel/wheel.cgi</a>.</p

The CD spectra of the peptides.

<p>The peptides were dissolved in 10 mM PBS (pH 7.4) (dashed lines), 50% TFE (triangles), or 30 mM SDS (squares). The mean residue ellipticity was plotted against wavelength. The values from three scans were averaged per sample, and the peptide concentrations were fixed at 150 µM.</p

Antibiofilm activities of the peptides.

<p>A) Biomass of <i>P. aeruginosa</i> 27853 biofilms were reduced after 24 h treatment with various concentrations of LL37 and T9W relative to the untreated control. B) FE-SEM images of <i>P. aeruginosa</i> 27853 biofilms treated with the peptides at their 4×MICs.</p

Confocal fluorescence microscopic images of <i>P. aeruginosa</i> 27853 cells treated with FITC-labeled peptides at 37°C for 60 min.

<p>Panels on the left, middle and right represent laser-scanning, transmitted light-scanning, and merged images of cells treated with FITC-labeled peptides, respectively.</p

The cytoplasmic membrane potential variation of <i>P. aeruginosa</i> 27853 treated by peptides at concentrations of 0 (open circles), 0.8 (solid circles), 1.6 (triangles), 3.2 (squares), and 6.4 (rhombus) µM, as assessed by release of the membrane potential-sensitive dye diSC₃-5.

<p>The fluorescent intensity was monitored at an excitation wavelength of 622 nm and an emission wavelength of 670 nm as a function of time.</p

Combating Drug-Resistant Fungi with Novel Imperfectly Amphipathic Palindromic Peptides

Antimicrobial peptides are an important weapon against invading pathogens and are potential candidates as novel antibacterial agents, but their antifungal activities are not fully developed. In this study, a set of imperfectly amphipathic peptides was developed based on the imperfectly amphipathic palindromic structure R_<i>n</i>(XRXXXRX)­R_<i>n</i> (<i>n</i> = 1, 2; X represents L, I, F, or W), and the engineered peptides exhibited high antimicrobial activities against all fungi and bacteria tested (including fluconazole-resistant <i>Candida albicans</i>), with geometric mean (GM) MICs ranging from 2.2 to 6.62 μM. Of such peptides, <b>13</b> (I6) (RRIRIIIRIRR-NH₂) that was Ile rich in its hydrophobic face had the highest antifungal activity (GM_fungi = 1.64 μM) while showing low toxicity and high salt and serum tolerance. It also had dramatic LPS-neutralizing propensity and a potent membrane-disruptive mechanism against microbial cells. In summary, these findings were useful for short AMPs design to combat the growing threat of drug-resistant fungal and bacterial infections

Combating Drug-Resistant Fungi with Novel Imperfectly Amphipathic Palindromic Peptides

Antimicrobial peptides are an important weapon against invading pathogens and are potential candidates as novel antibacterial agents, but their antifungal activities are not fully developed. In this study, a set of imperfectly amphipathic peptides was developed based on the imperfectly amphipathic palindromic structure R_<i>n</i>(XRXXXRX)­R_<i>n</i> (<i>n</i> = 1, 2; X represents L, I, F, or W), and the engineered peptides exhibited high antimicrobial activities against all fungi and bacteria tested (including fluconazole-resistant <i>Candida albicans</i>), with geometric mean (GM) MICs ranging from 2.2 to 6.62 μM. Of such peptides, <b>13</b> (I6) (RRIRIIIRIRR-NH₂) that was Ile rich in its hydrophobic face had the highest antifungal activity (GM_fungi = 1.64 μM) while showing low toxicity and high salt and serum tolerance. It also had dramatic LPS-neutralizing propensity and a potent membrane-disruptive mechanism against microbial cells. In summary, these findings were useful for short AMPs design to combat the growing threat of drug-resistant fungal and bacterial infections