Browsing by Author "Yang, Lin"
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Item Cooperative phenomena of antimicrobial peptides in membranes: A study by neutron and X-ray diffraction(2001) Yang, Lin; Huang, Huey W.Gene-encoded membrane-active antimicrobial peptides permeablize bacterial plasma membranes without harming the host cells. Furthermore, although most peptides exhibit a broad spectrum of activity against microbes, different peptides preferentially kill different pathogens. Understanding such cell-type specificity is not only fundamental to cell biology but also crucial to potential pharmaceutically applications of antimicrobial peptides. Accumulated evidence indicates that the antimcrobial peptides target the lipid matrix of the plasma membranes. Therefore we focus on the physical states of the peptides bound to lipid bilayers. This thesis describes studies of lipid-peptide systems in the form of aligned multi-lamellae with new neutron and X-ray diffraction techniques developed specifically for such systems, under various conditions with improved temperature and relative humidity control. These technique allow the most detailed structural investigation on the supramolecular assemblies formed by these peptides in model lipid membranes. Interesting phenomena were observed. Peptides form transmembrane pores in fluid lipid bilayers. The sizes of various peptide pores were determined by fitting neutron scattering data with the theory of scattering. By manipulating the temperature and the hydration level of the samples, we observed position correlations developed between the pores located in neighboring bilayers that eventually became long-range and the transmembrane pores were crystallized in lipid membranes for the first time. Diffraction data of the crystallized pores were measured with synchrotron radiation using samples on ultra-thin Si3N4 substrate for transmission X-ray diffraction. A number of different crystalline phases were found. One example is the ABC stacking hexagonal structure, surprisingly also found in pure diphytanoyl phosphatidylcholine samples. Correlating the diffraction data with circular dichroism and other experimental evidence, we separate the pore structures into two categories described by the barrel-stave model and the toroidal model. The implication of these results on the peptide's cell-type specificity is also discussed in terms of the properties of the lipids and environmental variables.Item High Concentration Organic Wastewater with High Phosphorus Treatment by Facultative MBR(MDPI, 2021) Wang, Bing; Liu, Yunlong; Zhang, Siyu; Zhang, Kaihang; Alvarez, Pedro; Crittenden, John C.; Sun, Bing; Yang, Lin; Liu, Su; Ran, ZhilinPhosphorus is one of the main factors causing water eutrophication, and the traditional phosphorus removal process causes phosphorus-rich sludge pollution. The facultative MBR process uses phosphate-reducing bacteria to convert phosphate into directly recyclable gaseous phosphine to solve this malpractice and make sewage become a new phosphorus resource. In order to investigate the phosphorus removal efficiency and the mechanism under facultative conditions, run the facultative MBR reactor for 30 days. The COD value, phosphate concentration, and phosphine yield were measured, and the changes of sludge metabolic pathway abundance and community composition in different periods were detected. According to the measurement, the maximum phosphorus removal efficiency is 43.11% and the maximum yield of phosphine is 320 μg/m3 (measured by the volume of sewage). Combined with thermodynamic analysis, the microbial mechanism of the reactor was proposed, and the possible transformation pathway of phosphorus was analyzed. At last, changes the phosphorus removal process from the ‘removal type’ to the ‘recycling type’.Item Neutron off-plane scattering of aligned membranes(1998) Yang, LinOur group studies the interaction between antibiotic peptides and phospholipids. These peptides are known to form channels in the lipid membrane. With X-ray diffraction, oriented circular dichroism and in-plane neutron scattering measurements, and evidences from experiments done by others, we have established channel models for alamethicin and magainin, and measured the channel sizes. In this thesis, neutron off-plane scattering of aligned peptide-lipid samples is discussed. Compared to in-plane scattering, this new technique provides a much richer structural information of the sample. We therefore are able to easily distinguish different structures based on the scattering pattern, and, ideally, reconstruct the channel scattering length density in real space. Inter-membrane correlation was observed in the magainin samples.