It is generally accepted that N-glycans are important to the overall stability of glycoproteins [reviewed in [22]]. Our observations that the mature/fully glycosylated A118/N40-hMOPR had a longer half-life than those of G118/D40-hMOPR are consistent with this notion. These results are in accord with the findings on several 7TMRs, including the human kappa opioid receptor [23], vasopressin 1a receptor [24] and protease-activated receptor-2 [25]. For example, mutation of the two N-linked glycosylation sites of hKOPR (hKOPR-N25/39Q) led to faster degradation of the mature mutant receptor and thereby decreased receptor expression. One notable difference is that the effects observed with A118G in the hMOPR are due to elimination of only one of the five consensus glycosylation sites, whereas those found for other 7TMRs resulted from total elimination of N-linked glycosylation.
