Structural characterization of membrane proteins in model membrane systems

Joe Blasic and Ella Mihailescu

Membrane proteins (MPs) are the main conduits through which information and materials are transmitted across cell membranes.  MPs have diverse functions, serving as ion channels, receptors, transporters, water channels, enzymes, cellular adhesion molecules and structural anchors for other proteins.  In the membrane, these proteins are surrounded by a shell of interacting lipids called annular lipids, which are tightly associated with the protein to prevent leakage of solutes across the membrane.  Interactions between the protein and surrounding lipids lead to changes in the structure and organization of the membrane and affect the structure and function of the protein.  For most biochemical and structural analysis, these proteins must be separated from the membrane by extraction in detergent or non-polar solvents, as they are insoluble in aqueous solution, causing a loss of these important protein-lipid interactions.  Removal from the membrane environment leads to a loss of function for most MPs and can lead to misfolding or aggregation.  Due to the difficulties of working with these proteins, less than 0.5% of unique protein structures deposited in the protein data bank are of MPs.  I am working with a variety of biophysical methods to examine membrane protein structures in model membrane systems.  We are using a combination of neutron and X-ray diffraction as well as small angle neutron and X-ray scattering (SANS/SAXS) surface plasmon resonance (SPR) spectroscopy and neutron reflectometry to gain novel insights into membrane protein structure in model membrane systems.