Potassium channels are proteins embedded in the lipid bilayer that selectively allow K+ ion movement across the plasma membrane. Under physiological conditions K+ ion movement retards cellular excitability. A decrease in excitability can be manifested in different ways, such as in a decrease of the frequency of action potentials, the units of cellular electrical activity, or a decrease in transmitter release. A certain class of K+ channels, the G protein-gated K channels, couple extracellular signals, such as hormones or neurotransmitters, to changes in membrane potential and therefore to cellular excitability. Acetylcholine (ACh) for example, the transmitter of the vagus nerve, binds a receptor on the surface of a cardiac cell and activates a membrane associated signaling protein, called a GTP binding protein, which in turn interacts with the K+ channel to activate it and slow heart rate. The details of the interaction of the G protein with the potassium channel are not understood. This is partly due to lack of high resolution structures of mammalian K+ channels and their complex with the G proteins. Such information is of paramount importance in order to understand the molecular physiology of these potassium channels. This proposal seeks to understand how functionally important sites on G protein-gated K+ channels interact with G proteins. Use of an ion channel to probe G protein effects enables us to probe physiologically relevant interactions in real time and at an unprecedented resolution, the single protein level. Recently, we identified G protein sensitive sites of the k+ channel. In parallel we have developed computational methods to model the 3-D structure of a G protein-interacting peptide, QEHA (Chen et al., 1995). Here, we propose subjecting the channel G protein-sensitive peptides to Monte Carlo/Stochastic Dynamics simulations and testing experimentally model predictions, in order to understand their interactions with G proteins. What makes this proposal unique and most appropriate for funding by the National Science Foundation is the exciting collaboration of theoretical and experimental approaches lead by the two co-investigators.
