Interactions of the C Terminus of Metabotropic Glutamate Receptor Type 1α with Rat Brain Proteins

: Metabotropic glutamate receptors (mGluRs) are coupled toG protein second messenger pathways and modulate glutamate neurotransmissionin the brain, where they are targeted to specific synaptic locations. As partof a strategy for defining the mechanisms for the specific targeting of mGluR1α, rat brain proteins which interact with the intracellular carboxyterminus of mGluR1 α have been characterized, using affinitychromatography on a glutathione S ‐transferase fusion protein thatcontains the last 86 amino acids of mGluR1 α. Three of the proteinsspecifically eluted from the affinity column yielded protein sequences, two ofwhich were identified as glyceraldehyde‐3‐phosphate dehydrogenase andβ‐tubulin ; the other was an unknown protein. The identity of tubulin wasconfirmed by western immunoblotting. Using a solid‐phase binding assay, themGluR1 α‐tubulin interaction was shown to be direct, specific, andsaturable with a K D of 2.3 ± 0.4 μ M . In addition, mGluR1 α, but not mGluR2/3 or mGluR4, could be coimmunoprecipitated from solubilized brain extracts with tubulin using anti‐β‐tubulin antibodies. However, mGluR1 α could not be coimmunoprecipitated with the tubulin binding protein gephyrin, nor could it be coimmunoprecipitated with PSD95. Collectively these data demonstrate that the last 86 amino acids of the carboxyl‐terminal tail of mGluR1 α are sufficient to determine its interaction with tubulin and that there is an association of this receptor with tubulin in rat brain.