The present invention relates to polypeptides capable of modulating odorant receptor activation. In particular, the present invention provides polypeptides (e.g., type 3 muscarinic actetylcholine receptor M3) capable of enhancing odorant receptor activation. The present invention further provides assays for the detection of ligands specific for various odorant receptors. Additionally, the present invention provides methods of screening for polypeptide polymorphisms and mutations associated with odorant receptor activation (e.g., polymorphisms and mutations associated with muscarinic actetylcholine receptor polypeptides (e.g., M1, M2, M3, M4, M5)), as well as methods of screening for therapeutic agents, ligands, and modulators of such proteins.