G[gamma]13 Interacts with PDZ Domain-containing Proteins

The G protein [gamma]13 subunit (G[gamma]13) is expressed in taste and retinal and neuronal tissues and plays a key role in taste transduction. We identified PSD95, Veli-2, and other PDZ domain-containing proteins as binding partners for G[gamma]13 by yeast two-hybrid and pull-down assays. In two-hybrid assays, G[gamma]13 interacted specifically with the third PDZ domain of PSD95, the sole PDZ domain of Veli-2, and the third PDZ domain of SAP97, a PSD95-related protein. G[gamma]13 did not interact with the other PDZ domains of PSD95. Coexpression of G[gamma]13 with its G[beta]1 partner did not interfere with these two-hybrid interactions. The physical interaction of G[gamma]13 with PSD95 in the cellular milieu was confirmed in pull-down assays following heterologous expression in HEK293 cells. The interaction of G[gamma]13 with the PDZ domain of PSD95 was via the C-terminal CAAX tail of G[gamma]13 (where AA indicates the aliphatic amino acid); alanine substitution of the CTAL sequence at the C terminus of G[gamma]13 abolished its interactions with PSD95 in two-hybrid and pull-down assays. Veli-2 and SAP97 were identified in taste tissue and in G[gamma]13-expressing taste cells. Coimmunoprecipitation of G[gamma]13 and PSD95 from brain and of G[gamma]13 and SAP97 from taste tissue indicates that G[gamma]13 interacts with these proteins endogenously. This is the first demonstration that PDZ domain proteins interact with heterotrimeric G proteins via the CAAX tail of G[gamma] subunits. The interaction of G[gamma]13 with PDZ domain-containing proteins may provide a means to target particular G[beta][gamma] subunits to specific subcellular locations and/or macromolecular complexes involved in signaling pathways.