Identification of Proteins Interacting with mGluR6

Metabotropic glutamate receptors (mGluRs) are a family of 8 G protein coupled receptors that can be divided into three different groups. Group III mGluRs, which includes mGluR6, couple exclusively to the pertussis toxin (PTX)‐sensitive Gαi/o family of heterotrimeric G proteins. mGluR6 plays a unique role in the visual system by acting as the primary postsynaptic neurotransmitter receptor in ON Bipolar cells, which receive glutamatergic input directly from photoreceptor cells. Activation of mGluR6 initiates a signaling cascade, leading to inhibition of a cation channel and cell hyperpolarization. However, the role of specific members of the Gαi/o family in functionally coupling to mGluR6 remains unclear. By using a reconstitution system in sympathetic neurons from the rat superior cervical ganglion, coupling of heterologously expressed mGluR6 with PTX‐insensitive mutant Gαi/o proteins was investigated. We found that mGluR6 couples strongly to Gαoa (consistent with previous studies), moderately to Gαob and Gαi1, and weakly to Gαi2 and Gαi3. No coupling was detected with Gαz, Gαtransducin(rod) or Gαtransducin(cone). Many GPCRs can interact with specific intracellular proteins that play key roles in regulating their signaling properties. To identify such potential regulators for mGluR6, we developed yeast two‐hybrid screens using the second intracellular loop, the third intracellular loop, and the C‐terminus of mGluR6 as baits against a rat retinal cDNA library. These screens identified 4 distinct proteins as potential mGluR6 regulators. Preliminary characterization of these proteins as regulators of mGluR6 function in our sympathetic neuron reconstitution system will be presented.