A new electrophoretic method is proposed for efficiently separating membrane proteins while retaining function. Fluid, smooth, electrically neutral lipid bilayers are proposed as the electrophoretic medium. The proposed separation would maintain the membrane proteins in their natural type of environment to produce separated zones of membrane proteins, which are then displayed as functional arrays. The separation would support such applications as membrane proteomics, drug screening and development of cancer diagnostics. Membrane proteins play key roles in human health, since they direct cellular signaling, recognition and transport, yet the steps for isolating membrane proteins for research are expensive, laborintensive and inefficient. Today's methods for separating proteins rely on water solubility. The proposed work will test the feasibility of separating membrane proteins in lipid bilayers by investigating 3 essential properties. First, the fluidity and uniformity of the lipid bilayer will be studied on ultrasmooth polyacrylamide films, grown by atom-transfer radical polymerization. The polyacrylamide film provides a uniform hydrophilic boundary on the underside of the bilayer, an aqueous buffer will be used on the upper side. Second, the electrophoretic mobilities of 5 well characterized receptors will be studied: the 3 opioid receptors and 2 melanocortin receptors. All 5 are medically important G-protein coupled receptors. Their ligands are peptides, which will be singly labeled with rhodamine. Third, the function of these membrane proteins will be studied by single-molecule fluorescence spectroscopy of the rhodamine labeled ligands. The R21 research will critically test the idea of whether the electrophoretic separation of functional membrane proteins is feasible in supported lipid bilayers. If feasible, an R01 proposal would address separations of real mixtures of membrane proteins from cell lysates. The work could have enormous impact on drug discovery, allowing inexpensive screening that encompasses many receptors.
