PALMITOYLATION OF THE GLUR6 KAINATE RECEPTOR

The G-protein-coupled metabotropic glutamate receptor mGluR1 alpha and the ionotropic glutamate receptor GluR6 were examined for posttransla tional palmitoylation, Recombinant receptors were expressed in baculov irus-infected insect cells or in human embryonic kidney cells and were metabolically labeled with [H-3]palmitic acid. The metabotropic mGluR 1 alpha receptor was not labeled whereas the GluR6 kainate receptor wa s labeled after incubation with [H-3]palmitate, The [H-3]palmitate lab eling of GluR6 was eliminated by treatment with hydroxylamine, indicat ing that the labeling was due to palmitoylation at a cysteine residue via a thioester bond, Site-directed mutagenesis was used to demonstrat e that palmitoylation of GluR6 occurs at two cysteine residues, C827 a nd C840, located in the carboxyl-terminal domain of the molecule. A co mparison of the electrophysiological properties of the wild-type and u npalmitoylated mutant receptor (C827A, C840A) shelved that the kainate -gated currents produced by the unpalmitoylated mutant receptor were i ndistinguishable from those of the wild-type GluR6, The unpalmitoylate d mutant,vas a better substrate for protein kinase C than the wild-typ e GluR6 receptor. These data indicate that palmitoylation may not modu late kainate channel function directly but instead affect channel func tion indirectly by regulating the phosphorylation state of the recepto r.