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J Mol Biol. 2011 Jun 17;409(4):513-28. doi: 10.1016/j.jmb.2011.03.059. Epub 2011 Apr 6.

Differential interactions of fluorescent agonists and antagonists with the yeast G protein coupled receptor Ste2p.

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  • 1Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.


We describe a rapid method to probe for mutations in cell surface ligand-binding proteins that affect the environment of bound ligand. The method uses fluorescence-activated cell sorting to screen randomly mutated receptors for substitutions that alter the fluorescence emission spectrum of environmentally sensitive fluorescent ligands. When applied to the yeast α-factor receptor Ste2p, a G protein-coupled receptor, the procedure identified 22 substitutions that red shift the emission of a fluorescent agonist, including substitutions at residues previously implicated in ligand binding and at additional sites. A separate set of substitutions, identified in a screen for mutations that alter the emission of a fluorescent α-factor antagonist, occurs at sites that are unlikely to contact the ligand directly. Instead, these mutations alter receptor conformation to increase ligand-binding affinity and provide signaling in response to antagonists of normal receptors. These results suggest that receptor--agonist interactions involve at least two sites, of which only one is specific for the activated conformation of the receptor.

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