Identification of the Gbeta5-RGS protein complex in retina

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Molecular and Cellular Pharmacology

First Committee Member

Vladlen Slepak - Committee Chair


G-proteins couple membrane-bound receptors to intracellular effectors. Each cell has a characteristic complement of G alpha subunits (Galpha) and beta-gamma complexes (Gbetagamma), that partly determines the cell's response to external signals. Stimulation of cell surface receptors promotes dissociation of Galpha from the Gbetagamma dieter. This allows both components to interact and modulate the activity of intracellular enzymes or ion channels. The Gbeta subunit family, in contrast to the less conserved Galpha and Ggamma families is extremely homologous (over 90% identical) with the exception of Gbeta5. Gbeta5 deviates significantly from the four other members of the Gbeta subunit family in amino acid sequence. Gbeta5 also has a unique expression pattern (only in the CNS), and cytosolic localization. In order to delineate the Gbeta5 mediated signaling pathway, I purified and identified proteins complexed with Gbeta5 from cytosolic fractions of bovine retina. Mass spectral analysis of the isolated complex revealed that Gbeta5 associates with an RGS protein, a member of the superfamily of negative regulators of Galpha signaling. This finding is the first description of an interaction between a Gbeta subunit and an RGS protein. Even more interesting is the fact that I show in native tissue that this Gbeta5-RGS complex does not contain a G protein gamma subunit. My third finding suggests the Gbeta5-RGS interaction blocks the binding of RGS7 to the Galpha subunit Galphao, and hence may act as an inhibitor of the pathway mediated by either Gbeta5 or an RGS.


Biology, Molecular

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