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- Manioglu, S., et al.
(författare)
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Antibiotic polymyxin arranges lipopolysaccharide into crystalline structures to solidify the bacterial membrane
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Polymyxins are last-resort antibiotics with potent activity against multi-drug resistant pathogens. They interact with lipopolysaccharide (LPS) in bacterial membranes, but mechanistic details at the molecular level remain unclear. Here, we characterize the interaction of polymyxins with native, LPS-containing outer membrane patches of Escherichia coli by high-resolution atomic force microscopy imaging, along with structural and biochemical assays. We find that polymyxins arrange LPS into hexagonal assemblies to form crystalline structures. Formation of the crystalline structures is correlated with the antibiotic activity, and absent in polymyxin-resistant strains. Crystal lattice parameters alter with variations of the LPS and polymyxin molecules. Quantitative measurements show that the crystalline structures decrease membrane thickness and increase membrane area as well as stiffness. Together, these findings suggest the formation of rigid LPS-polymyxin crystals and subsequent membrane disruption as the mechanism of polymyxin action and provide a benchmark for optimization and de novo design of LPS-targeting antimicrobials. Manioglu et al use high-resolution atomic force microscopy to resolve how polymyxins interact with the bacterial membrane. Polymyxins arrange the bacterial lipids into regular hexagonal structures that stiffen the membrane and lead to rupture.
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- Modaresi, M., et al.
(författare)
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Efficient optimization of a Yagi-Uda antenna using genetic algorithm
- 2017
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Ingår i: ANTEM 2005 - 11th International Symposium on Antenna Technology and Applied Electromagnetics, Conference Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). - 9780973842500
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Konferensbidrag (refereegranskat)abstract
- In this paper, Yagi-Uda antenna is studied and analyzed considering a single mode cosine current distribution on all elements. A classical approach is taken for the analysis, by viewing Yagi antenna as a center-driven dipole array in which all but the actual exciter element are short-circuited at the terminals. Currents are induced in the elements via the mutual impedances, and radiation occurs as from a set of discrete sources. The mutual impedance matrix of the array is calculated using the induced EMF method and integral equations for the electric field. This analysis has led to a fast and efficient code to calculate Yagi parameters. The validity of the results has been checked with a MoM solution using NEC2 and good agreement has been observed. Then, the code is used together with a genetic algorithm in order to optimize Yagi-Uda antenna for gain maximization. A 31-element high gain Yagi with 19.2dB gain and the gain bandwidth of 8 percent is derived. Also the Pareto fronts are plotted for Yagi antennas with different number of elements which shows the trade off between the directivity and front to back lobe(F/B) ratio.
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