G protein signaling in neurons was originally described as a linear sequence in which agonist bound to a specific receptor. which in turn activated a single species of G protein. That G protein then went on to activate or inhibit intracellular effectors such as adenylyl cyclase, phospholipase or various ion channels. Over the past several years, it has become clear that G protein signaling is a complex process. Some of this complexity involves direct regulation of receptors and G proteins by a variety of molecules that bind to or phosphorylate receptors (arrestins and receptor kinases) or increase GTPase activity of G proteins (RGS proteins). A more subtle form of regulation appears to be from a series of proteins and lipids that alter the positioning of the molecules of the G protein cascade on the membrane. Some of these are passive positioning molecules, but others, such as microtubules, offer dynamic interactions that both position and activate G proteins. The interface between G proteins and microtubules is bidirectional, as certain fty subunits stabilize microtubules, while a subunits promote rapid microtubule depolymerization. G proteins are highly concentrated at the post-synaptic density and it is hypothesized that their activation leads to cytoskeletal rearrangement and rapid synaptic shape change. It is in this framework, that research is proposed to explore the relationship of structure and function within the context of G protein signaling. Several imaging tools for both G proteins and microtubules will be used in experiments designed to discover the interplay between these systems. These techniques will be combined with the enzyme assays and the photoaffinity labeling we have used successfully to probe the activation of G proteins and the functional activity of fluorescent (normal and mutant) G proteins in cells and in mice. G protein coupled receptors and their downstream effects are favorite targets of current neuropharmacology. By developing a better understanding of the relationship of those receptors and G proteins to the neuronal microenvironment, new therapeutic strategies for the diseases of brain and mind are likely to be forthcoming.
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