Heterotrimeric G proteins mediate signaling across the plasma membranes of cells for many hormones and neurotransmitters, as well as for a wide variety of other regulatory agents. They are known or likely sites for disease processes such as cholera and pertussis, and their role in cellular regulation makes them likely contributors to the pathology, if not etiology, of complex diseases such as diabetes, essential hypertension and cancer. Understanding how these proteins function in normal signaling events is essential to describing their role in disease states and to providing information about the future possible development of these proteins as targets for pharmacologic intervention. One of the two main hypotheses upon which this research is based is that the widespread involvement of these proteins in cell signaling depends upon the immense structural and functional diversity of the G protein subunits. A primary objective of the proposed studies is to define the role of subunit diversity in signaling by heterotrimeric G proteins. Thus, the first two Specific Aims are: (1) To determine the origin and nature of the structural diversity of the beta and gamma subunits of G proteins. These studies take advantage of protein chemistry and mass spectrometry expertise associated with this project. (2) To determine the functional differences between Gbetagamma dimers containing (a) different beta or gamma isoforms or (b) differently modified gamma subunit isoforms. These studies use primarily molecular biology approaches to apply the information generated under Specific Aim 1 to the biochemical characterization of the G protein subunits. An important functional step in the action of G proteins is the GTP-dependent dissociation of their a subunit from their associated betagamma dimer. This reaction has diverse implications for the cellular signaling processes mediated by G proteins, in large part due to their structural and functional diversity. We hypothesize that G protein subunit dissociation is a key step in signal transduction that can determine to what signals cells respond, as well as the nature of that response. To test this hypothesis the third Specific Aim is: (3) To determine the physiological role of subunit dissociation in intact membranes and intact cells. These studies will specifically test whether the G protein subunit diversity characterized under Specific Aims 1 and 2 is utilized by cells to generate changing patterns of G protein heterotrimers with varying signaling properties. The results of this project will define the potential range of functional diversity associated with these proteins, and in so doing define their diversity as potential drug targets.
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