Stargazin Interaction with α-Amino-3-hydroxy-5-methyl-4-isoxazole Propionate (AMPA) Receptors Is Critically Dependent on the Amino Acid at the Narrow Constriction of the Ion Channel

Abstract

The subunit GluR2 of the ␣-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subfamily of ionotropic glutamate receptors (GluRs) features a single amino acid at the narrow constriction of the pore loop that is altered from glutamine to arginine by RNA editing. This so-called Q/R site has been shown to play an important role in the determination of the electrophysiological properties of AMPA receptor complexes as well as of trafficking to the plasma membrane. The protein stargazin has also been shown to modulate electrophysiological properties and trafficking to the plasma membrane of AMPA receptors. In this study we examined via a series of mutants of the Q/R site of the AMPA receptor GluR1 whether the amino acid at this position has any influence on the modulatory effects mediated by stargazin. To this end, we analyzed current responses of Q/R site mutants upon application of glutamate and kainate and determined the amount of mutant receptor protein in the plasma membrane in Xenopus oocytes. Desensitization kinetics of several mutants were analyzed in HEK293 cells. We found that the stargazin-mediated decrease in receptor desensitization, the slowing of desensitization kinetics, and the kainate efficacy were all dependent on the amino acid at the Q/R site, whereas the stargazin-mediated increase in trafficking toward the plasma membrane remained independent of this amino acid. We propose that the Q/R site modulates the interaction of stargazin with the transmembrane domains of AMPA receptors via an allosteric mechanism and that this modulation leads to the observed differences in the electrophysiological properties of the receptor.

Altered AMPA receptor expression with treadmill exercise in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned mouse model of basal ganglia injury

“…LTD expressed at the parallel fiber synapse with cerebellar Purkinje cells is mediated via phosphorylation of GluR2-Ser880 and subsequent internalization and retention of the receptor through its interaction with accessory proteins (Song and Huganir, 2002;Seidenman et al, 2003;Kakegawa and Yuzaki, 2005;Tomita et al, 2005;Korber et al, 2007;Lin and Huganir, 2007). Findings from our study suggest that exercise-based motor training alters synaptic strength and that this may be achieved, in part, by trafficking of AMPARs, which could lead to sustained changes in synaptic plasticity (Malinow and Malenka, 2002;Song and Huganir, 2002;Bredt and Nicoll, 2003;Jiang et al, 2006).…”

Regulation of Ionotropic Glutamate Receptors by Their Auxiliary Subunits

“…In addition, TARPs render AMPARs more inwardly rectifying channels (11, 72, 73). Mutations in the channel pore of AMPARs changed the magnitude of TARP modulation of AMPAR activity (36). These observations suggest that TARPs may change the molecular environment surrounding the AMPAR-channel pore.…”

Regulation of AMPA receptors and synaptic plasticity

“…Stargazin and other transmembrane (TM) AMPA receptor regulatory proteins (TARPs) also coassemble stoichiometrically with native AMPARs. The TARPs act as auxiliary subunits that are required for AMPAR maturation and trafficking, and modulate channel function (see below) (Korber et al, 2007;Ziff, 2007).…”