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. In deed, a growing number of G protein-coupled receptors (rhodopsin, beta (2-), and alpha(2)-adrenergic receptors) have now been shown to have p almitic 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 t his receptor to interact with and activate Gs. Mutation of this conser ved cysteine appears to have little or no effect on the ability of oth er members of this receptor family (rhodopsin, alpha(2)-adrenergic and M2 muscarinic) to activate their cognate G proteins, however. The stu dies presented here were designed to determine whether another Os-coup led receptor, the LH/CG receptor, is palmitoylated, and whether this m odification is important for receptor function. To facilitate biochemi cal analysis, we examined these issues using cell lines stably transfe cted with the wild type LH/CG receptor (LHR-wt) or with a mutant recep tor in which the two conserved cysteins were mutated to alanines (desi gnated LHR-C621,622A). Our results show that LHR-wt is palmitoylated b ut that LHR-C621,622A is not. We also show that LHR-C621,622A is capab le 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 mat ure cell surface LH/CG receptor.