Inhibition of N-linked glycosylation of the human type 1alpha metabotropic glutamate receptor by tunicamycin: effects on cell-surface receptor expression and function

The potential role of N-linked glycosylation of the human type 1alpha metabotropic glutamate (mGlu1alpha) receptor was studied in a recombinant, inducible expression system, where receptor expression was induced in the absence and presence of tunicamycin. In the absence of tunicamycin the mGlu1alpha receptor appeared to be expressed, at least in part, as a dimer consisting of monomers of approx. 145 and 160 KDa relative molecular mass (Mr). In the presence of tunicamycin only a single monomeric protein could be detected approximating the Mr predicted for the human mGlu1alpha receptor based on its primary amino acid sequence (130 KDa). Exposure to tunicamycin during receptor induction did not appear to affect the cell surface expression of the mGlu1alpha receptor as determined immunocytochemically or using a cell-surface biotinylation strategy, but reduced agonist-stimulated phosphoinositide hydrolysis by approximately 50% compared to control cell populations. Our data suggest that non-N-glycosylated human mGlu1alpha receptors can traffic to the cell surface and activate phospholipase C.