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Identification of a novel protein partner of the M3 muscarinic acetylcholine receptor

The M3 muscarinic acetylcholine receptor is widely expressed throughout the central nervous system and is also found in many peripheral tissues and cell types. Several lines of work suggest that drugs acting on central or peripheral M3 receptors might become clinically useful in a variety of pathophysiological conditions. Recent evidence suggests that the function of many G protein‐coupled receptors (GPCRs) can be modulated by different classes of receptor‐interacting proteins. The objective of the present study was to identify proteins that can interact with central M3 muscarinic receptors. Recently, the split‐ubiquitin yeast two‐hybrid system has emerged as a novel approach to study membrane protein interactions. Using this system, we screened a human brain cDNA library using the full‐length M3 receptor as bait. We showed that the putative membrane protein Tmem147 heterodimerizes with the M3 receptor in COS7 cells using biochemical approaches. Confocal imaging studies showed that this interaction can occur in the ER as Tmem147 is not expressed at the plasma membrane. We hypothesize that Tmem147 may act as a previously unidentified chaperone in the ER. Given the lack of ligands that can selectively activate or block M3 receptors with high selectivity, the identification of novel protein partners may provide new insight into the regulation of M3 muscarinic receptor function and provide possible new drug targets.