Studies of Retinoschisin 1 on the membrane of retinal cell inner segments

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The combination of AFM and fluorescence can be a powerful tool for this type of project, where not only geometries but also identification of the imaged structures is critical. It is important to block non-specific binding of antibodies to the samples, and we are still fine tuning that process to optimize fluorescence imaging. A number of sample preparation methods have been tried to get as pure plasma membrane solutions as possible. We have successfully shown that the plasma membranes of the inner segments appear to have structured elements associated with them which have honeycomb-like structure. The identification of these structures with fluorescence proved more difficult so far, but ongoing work should optimize the appropriate conditions. We have recently been using artificial model supported bilayers to investigate the effects of RS1 absorption to the bilayers under different ionic conditions. We observe that, for bilayers composed of phosphatidylserine, an anionic lipid, protein adsorption in the presence of calcium, dramatically alters the topology of the bilayer and it appears that RS1 forms protein rich domains. In mixed lipids made of phosphatidylserine and phosphatidylcholine (1:3), the protein strongly binds to boundary defects but also forms small protein-rich domains at random locations. It appears, therefore, that RS1 binds to anionic lipids and the combination with fluoresence will help validate this hypothesis. The protein construct used is a product of RS1 expression in e-Coli and, as such, it appears that it possesses two folding conformations whose effects on the bilayers are somewhat different.