THE LUTROPIN/CHORIOGONADOTROPIN RECEPTOR IS PALMITOYLATED AT INTRACELLULAR CYSTEINE RESIDUES

Most members of the family of G protein-coupled receptors have one or more conserved cysteine residues in their carboxy-terminal cytoplasmic tails which are believed to be consensus sites for palmitoylation. Indeed, a growing number of G protein-coupled receptors (rhodopsin, beta(2-), and alpha(2)-adrenergic receptors) have now been shown to have palmitic acid covalently attached to this position. In the case of the beta(2)-adrenergic receptor, it was also reported that mutation of the palmitoylated cysteine to glycine greatly diminished the ability of this receptor to interact with and activate Gs. Mutation of this conserved cysteine appears to have little or no effect on the ability of other members of this receptor family (rhodopsin, alpha(2)-adrenergic and M2 muscarinic) to activate their cognate G proteins, however. The studies presented here were designed to determine whether another Os-coupled receptor, the LH/CG receptor, is palmitoylated, and whether this modification is important for receptor function. To facilitate biochemical analysis, we examined these issues using cell lines stably transfected with the wild type LH/CG receptor (LHR-wt) or with a mutant receptor in which the two conserved cysteins were mutated to alanines (designated LHR-C621,622A). Our results show that LHR-wt is palmitoylated but that LHR-C621,622A is not. We also show that LHR-C621,622A is capable of binding human CG (hCG) and transducing the cAMP signal. The main difference that we detected between the wild type and mutant receptor is that the latter is trapped intracellularly and does not appear to mature into the 85 kilodalton protein previously identified as the mature cell surface LH/CG receptor.