Membrane Biology

The most basic requirement for life is compartmentalization. Without membranes to keep all the necessary soluble molecular components of life in a defined area, individual cells and multicellular organisms (e.g. humans) could not exist.  Biological membranes are complex superstructures that perform many tasks other than compartmentalization.  They are composed of thousands of different molecules that are assembled in a carefully defined manner and to a tightly controlled makeup.  Each membrane has its own characteristic composition depending on its functions.  In the case of mammalian cells, the protein and lipid makeup of a plasma membrane is quite different from that of the mitochondrial and nuclear membranes.

A number of investigators within the department investigate the biosynthesis, function and physical characteristics of membranes.

Raphael A. Zoeller, Ph.D. – Complex lipid biosynthesis, metabolism and transport

Animal cell membranes contain a wide variety of lipid species.  Each membrane displays a characteristic lipid composition, depending upon the cell type and the location within the cell.  Changes to this “membrane homeostasis” lead to a variety of pathologies.  Our laboratory is focused on identifying factors that influence glycerolipid biosynthesis and transport, processes that regulate specific membrane compositions.  To do this we isolate and study mutant cell lines that show defects in lipid biosynthesis or transport. These mutant cells are used to identify functions for specific lipid species, to identify factors important for their biosynthesis and to isolate genes involved in lipid metabolism.  A variety of biochemical, structural and genetic techniques are used to characterize these mutant cell lines.

A number of these mutants have biochemical and genetic lesions identical to inherited human diseases and can therefore be used as models to study the molecular basis for the disease.

Key words: Animal cell mutants, phospholipids, human disease, plasmalogens, somatic cell genetics, expression cloning, tissue culture.

James A. Hamilton, Ph.D. – Fatty acid transport

Fatty acids represent a major source of dietary energy and a storage form of energy in adipose tissue. Some fatty acids have significant biological activity as second messengers and cytokines. Alterations in proteins that aid in fatty acid transport are associated with human disease such as diabetes.  We are therefore interested in the transport of these molecules within cells and the blood stream, their transport across biological membranes and the proteins that aid in these processes.  To do this, we use a variety of physical and instrumental techniques, including solution state 13C NMR spectroscopy, solid state and magic angle spinning multinuclear NMR, multidimensional NMR, NMR imaging, and fluorescence.

Donald M. Small, MD –Membrane structure and biophysics

Our interests cover the general area of the physical properties of fats and oils, detergents, lipids, proteins and lipid-protein interactions. Specific systems of interest include artificial membranes (bilayers), surfaces and cores of native lipoproteins, and recombinant lipoproteins using specific lipids and either native or genetically engineered apolipoproteins. A biophysical approach is used to probe disease processes such as athersclerosis, lipoproteinemias and gallstone formation. A wide variety of biophysical, biochemical and physiological methods are used to probe these problems.

G. Graham Shipley, Ph.D., D.Sc. – Membrane and receptor biology

Our interests center around the structure and function of cell membranes, receptor-ligand interactions and transmembrane signaling mechanisms. A combination of biochemical, chemical and biophysical approaches are used to probe: (1) membrane lipid conformation, structure, properties and interactions, (2) membrane receptor-lipid interactions and (3) membrane receptor-ligand interactions. Current approaches involve the isolation of membrane-associated proteins and lipids (e.g. low density lipoprotein (LDL) receptor, insulin receptor, integrins, gangliosides), their reconstitution with well characterized lipid monolayer and bilayer matrices and structural studies of the protein-lipid assemblies. Ligand binding studies include LDL receptor/LDL, insulin receptor/insulin, and ganglioside/toxin interactions. The biochemical methods involved include lipid and protein isolation, gel/affinity chromatography, antibody techniques, immunoblotting, detergent solubilization, lipid-protein reconstitution, etc. Chemical methods include lipid synthesis, TLC, HPLC, IR and NMR. The biophysical approach involves x-ray diffraction, protein crystallography, electron microscopy/image reconstruction, surface chemistry and calorimetric and spectroscopic (CD, NMR) methods.