The role of the light antenna protein LHC-II in the structure and dynamic reorganization of photosynthetic membranes

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BackgroundLipopolysaccharide (LPS) is a complex lipoglycan, which acts as a major structural component of the outer membrane of Gram-negative bacteria and potent toxin when released from cells ("endotoxin"). It is important that we understand LPS-lipid molecular interactions which may affect toxicity. We previously found that LPS inserts into model membranes and causes major perturbations: (i) lipid tubule formation, (ii) membrane perforation and (iii) multilayer formation. These changes were proposed to be governed by local electrostatic interactions, however, a detailed mechanism is required.Objectives(1) Elucidate the molecular basis of LPS-lipid interaction.(2) Qualify any correlation between pathogenicity of LPS source and membrane disruptiveness.(3) Determine physical property changes induced by LPS on membranes.(4) Test biologically-relevant inhibitors of LPS action.Novelty/TimelinessWe were the first group to observe perturbation of supported lipid bilayers by LPS and with our expertise in this system and required experimental techniques, we are uniquely-placed to reveal the underlying molecular mechanism. Whilst many have investigated either the pathogenicity (endotoxic shock) or isolated LPS (physical characterization), the dynamic changes caused by LPS on a combined lipid/LPS model system have not been fully investigated. Experimental approachState-of-the-art microscopy will be used to visualize dynamic membrane organizational changes at the nanoscale (atomic force microscopy (AFM), 1-nm-resolution at 8 fps) and track membrane fluidity (fluorescence microscopy). This will allow qualitative assessment of the effect of LPS from different bacteria (pathogenic/ non-pathogenic) on different lipid systems (charged, "lipid raft"-like). A quantitative analysis of physical changes induced by LPS on membranes will be undertaken using differential scanning calorimetry (melting transition temperatures), quartz crystal microbalance (mass/viscosity) and Langmuir trough measurements (membrane lateral pressure). Multilayers will be characterized with neutron reflectivity (layer thickness). Finally, various components of the immune system (e.g. LPS Binding Protein) will be screened for ability to inhibit LPS-induced damage.