Antimicrobial peptides (AMPs), which present in the non-specific immune system of organism, are amongst the most promising candidates for the development of novel antimicrobials. The modification of naturally occurring AMPs based on their residue composition and distribution is a simple and effective strategy for optimization of known AMPs. In this study, a series of truncated and residue-substituted derivatives of antimicrobial peptide PMAP-36 were designed and synthesized. The 24-residue truncated peptide, GI24, displayed antimicrobial activity comparable to the mother peptide PMAP-36 with MICs ranging from 1 to 4 µM, which is lower than the MICs of bee venom melittin. Although GI24 displayed high antimicrobial activity, its hemolytic activity was much lower than melittin, suggesting that GI24 have optimal cell selectivity. In addition, the crucial site of GI24 was identified through single site-mutation. An amino acid with high hydrophobicity at position 23 played an important role in guaranteeing the high antimicrobial activity of GI24. Then, lipid vesicles and whole bacteria were employed to investigate the membrane-active mechanisms. Membrane-simulating experiments showed that GI24 interacted strongly with negatively charged phospholipids and weakly with zwitterionic phospholipids, which corresponded well with the data of its biological activities. Membrane permeabilization and flow cytometry provide the evidence that GI24 killed microbial cells by permeabilizing the cell membrane and damaging membrane integrity. GI24 resulted in greater cell morphological changes and visible pores on cell membrane as determined using scanning electron microscopy (SEM) and transmission electron microscope (TEM). Taken together, the peptide GI24 may provide a promising antimicrobial agent for therapeutic applications against the frequently-encountered bacteria.
bAntimicrobial peptides with amphipathic -hairpin-like structures have potent antimicrobial properties and low cytotoxicity. The effect of VR or RV motifs on -hairpin-like antimicrobial peptides has not been investigated. In this study, a series of -hairpin-like peptides, Ac-C(VR) n D PG (RV) n C-NH 2 (n ؍ 1, 2, 3, 4, or 5), were synthesized, and the effect of chain length on antimicrobial activity was evaluated. The antimicrobial activity of the peptides initially increased and then decreased with chain length. Longer peptides stimulated the toxicity to mammalian cells. VR3, a 16-mer peptide with seven amino acids in the strand, displayed the highest therapeutic index and represents the optimal chain length. VR3 reduced bacterial counts in the mouse peritoneum and increased the survival rate of mice at 7 days after Salmonella enterica serovar Typhimurium infection in vivo. The circular dichroism (CD) spectra demonstrated that the secondary structure of the peptides was a -hairpin or -sheet in the presence of an aqueous and membrane-mimicking environment. VR3 had the same degree of penetration into the outer and inner membranes as melittin. Experiments simulating the membrane environment showed that Trp-containing VRW3 (a VR3 analog) tends to interact preferentially with negatively charged vesicles in comparison to zwitterionic vesicles, which supports the biological activity data. Additionally, VR3 resulted in greater membrane damage than melittin as determined using a flow cytometry-based membrane integrity assay. Collectively, the data for synthetic lipid vesicles and whole bacteria demonstrated that the VR3 peptide killed bacteria via targeting the cell membrane. This assay could be an effective pathway to screen novel candidates for antibiotic development.
Leucine (Leu) and isoleucine (Ile) have similar effects in the management of obesity and related disorders.
Currently, the majority of antibiotics in clinical use have broad activity spectra, killing pathogenic and beneficial microorganisms indiscriminately. The disruption of the ecological balance of normal flora often results in secondary infections or other antibiotic-associated complications. Therefore, targeted antimicrobial therapies capable of specifically eliminating pathogenic bacteria while retaining the protective benefits of a normal microflora would be advantageous. In this study, we successfully constructed a series of Enterococcus faecalis-targeted antimicrobial peptides from wide-spectrum antimicrobial peptide precursors. These peptides are designed based on fusion of the species-specific peptide pheromone cCF10 and modification of the active region of the antimicrobial peptide. The results showed that cCF10-C4 possessed specific antimicrobial activity against E. faecalis and was not active against other types of bacteria tested. The specificity of this hybrid peptide was shown by the absence of antimicrobial effects in the pheromone-substituted derivative. Further studies indicated that cCF10-C4 and its parent peptide C4 exert their activities by damaging cytoplasmic membrane integrity. the present study reveals the application potential of these molecules as "probiotic" antimicrobials for the control of specific bacterial infections, and it also helps to elucidate the design and construction of species-specific antimicrobials with precise targeting specificity. The mucosal surfaces and skins of animals are colonized by plenty of microorganisms. Most of the bacteria within the multispecies microbial community are beneficial 1. This indigenous flora plays a very important role in nutrient acquisition and protective colonization 2-4. Additionally, the normal flora represents an important ecological system, and alterations to the microflora may result in bacterial infections 5-7. Unfortunately, the majority of conventional antibiotics have wide activity spectra, killing pathogens and normal microflora indiscriminately and disrupting the micro-ecological balance. The unavoidable loss of microflora and ecological disruption resulting from antibiotic treatment may lead to severe and recurrent complications from persistent pathogens or opportunistic microorganisms that recolonize the vacated niche easily 8. The imbalance of normal microflora and the increasing threat of multidrug-resistant microbes highlight the urgent need for novel "targeted" antimicrobial therapies that can selectively eliminate pathogens without significantly disrupting resident normal flora. Antimicrobial peptides (AMPs) found in host immune systems have attracted considerable attention due to their excellent antimicrobial properties and unique action mechanism. These peptides are broad-spectrum with potent activities against microbes, viruses, parasites and even tumor cells 9-11. Furthermore, unlike traditional antimicrobial agents that inhibit specific metabolic pathways, the majority of antimicrobial peptides exert bactericidal effect...
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