Phosphorylation of ?3 glycine receptors induces a conformational change in the glycine-binding site.

ABSTRACT: Inflammatory pain sensitization is initiated by prostaglandin-induced phosphorylation of ?3 glycine receptors (GlyRs) that are specifically located in inhibitory synapses on spinal pain sensory neurons. Phosphorylation reduces the magnitude of glycinergic synaptic currents, thereby disinhibiting nociceptive neurons. Although ?1 and ?3 subunits are both expressed on spinal nociceptive neurons, ?3 is a more promising therapeutic target as its sparse expression elsewhere implies a reduced risk of side-effects. Here we compared glycine-mediated conformational changes in ?1 and ?3 GlyRs to identify structural differences that might be exploited in designing ?3-specific analgesics. Using voltage-clamp fluorometry, we show that glycine-mediated conformational changes in the extracellular M2-M3 domain were significantly different between the two GlyR isoforms. Using a chimeric approach, we found that structural variations in the intracellular M3-M4 domain were responsible for this difference. This prompted us to test the hypothesis that phosphorylation of S346 in ?3 GlyR might also induce extracellular conformation changes. We show using both voltage-clamp fluorometry and pharmacology that Ser346 phosphorylation elicits structural changes in the ?3 glycine-binding site. These results provide the first direct evidence for phosphorylation-mediated extracellular conformational changes in pentameric ligand-gated ion channels, and thus suggest new loci for investigating how phosphorylation modulates structure and function in this receptor family. More importantly, by demonstrating that phosphorylation alters ?3 GlyR glycine-binding site structure, they raise the possibility of developing analgesics that selectively target inflammation-modulated GlyRs.

SUBMITTER: Han L 

PROVIDER: S-EPMC3798985 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature