University of Virginia Health System

Dr. Gabor Szabo

Molecular interactions in G protein coupled signal transduction
Integration of extracellular signals is an essential function of the plasma membrane. For heptahelical receptors this function is accomplished by heterotrimeric G proteins that couple receptor activation to specific effectors. A major objective of the laboratory is to understand the physicochemical basis of the molecular interactions taking place during this signal transduction cascade. Total internal reflection fluorescence microscopy (TIRFM) of supported membranes is used to investigate interactions of fluorophore-labeled G protein and subunits with lipid membranes, either pure or incorporating molecules with which G proteins interact. Fluorescence intensity, fluctuation and energy transfer measurements are used to investigate molecular interactions in the membrane and to relate these to the structure of the protein and lipid components of the system.

Of particular interest are the functional roles of N-terminal myristoylation and thioacylation of G protein i/o subunits as well as lipids mimicking subdomains (rafts) of the plasma membrane. Proteins that associate with G proteins, including RGS, caveolin and a channel effector, are studied with respect to their effects on subunit lateral movement and interactions. In a complementary approach, excised patches of cell membranes expressing G protein-regulated muscarinic potassium channels (KACh) are used to assay the functionality of fluorescently labeled and/or chemically modified G protein subunits and to understand channel regulation in vivo on the basis of the TIRFM results. These studies are expected to establish a link between structural features of molecules participating in G protein coupled signaling and their functional dynamics.

Function of membrane proteins in pure lipid membranes
Synthetic lipid membranes made from pure lipids are used to understand the relationships between the structure and function of ion channels in membranes of well-defined composition. Channel forming molecules, including bacterial toxins and model peptides are incorporated in these membranes and studied under voltage clamp in order to understand their cellular function as it relates to their molecular structure.

Role of ion channels in the genesis and maintenance of atrial fibrillation
The laboratory is also interested to identify molecular events leading to a predisposition of the heart to atrial fibrillation (AF). Current focus is on atrial membrane currents that may be responsible for an increased vulnerability to fibrillation as well as the associated molecular and cellular factors that contribute to the maintenance and propagation of sustained AF. One of the goals of these studies is to design compounds that specifically target molecular pathways involved in the development of increased vulnerability to AF and test their efficacy.