ACS Chem. Neurosci., published online 8 July 2013; doi:10.1021/cn400097j

Glycine receptors (GlyRs) are pentameric ligand-gated ion channels that bind the neurotransmitter glycine at each of five extracellular subunit interfaces. Phosphorylation of Ser346 of GlyR α3 subunits by protein kinase A leads to chronic inflammatory pain sensitization and represents a focal point for designing drugs with analgesic activity. To identify unique structural features of α3 subunits that might permit selective drug design, Han et al. examined how α3 subunits differ from the widely expressed α1 GlyR subunits, which are not involved in pain sensitization. The authors monitored glycine-induced conformational changes in the two subunit types by voltage-clamp fluorometry, where the requisite environmentally sensitive fluorophore was placed at a common extracellular location in each subunit. These experiments revealed that, despite sharing a high amino acid sequence identity, α1 and α3 GlyRs adopt distinct quaternary structures. Using chimeras of the two subunits, the authors found that structural variations in the intracellular domain housing the Ser346 phosphorylation site were responsible for the different structures. Further voltage-clamp fluorometry experiments, including with the competitive antagonist tropisetron, showed that phosphorylation of Ser346 produced conformational changes that propagated all the way to the α3 glycine-binding site. These results suggest that chronic inflammatory pain sensitization produces a unique conformational change in the α3 glycine-binding site that could be exploited in the design of new therapeutics for chronic pain.