The Postendocytotic Trafficking of the Human Lutropin Receptor Is Mediated by a Transferable Motif Consisting of the C-Terminal Cysteine and an Upstream Leucine

Mutants of the human (h) lutropin receptor (LHR) were analyzed using a combination of biochemical and imaging approaches to define motifs that participate in the postendocytotic sorting of this G protein-coupled receptor (GPCR). We show that a substantial portion of the human chorionic gonadotropin internalized by the hLHR sorts to a recycling pathway, and the internalized hLHR accumulates in endosomes because of the C-terminal cysteine (Cys(699)) and an upstream Leu(683) present in the hLHR. The removal or simultaneous mutation of these two residues reroutes the internalized human chorionic gonadotropin to a degradation pathway and the internalized hLHR to lysosomes. We also show that grafting the 17 C-terminal residues of the hLHR into the C-terminal tail of two GPCRs that are routed to a lysosomal/degradation pathway (the rat LHR or the murine delta opioid receptor) reroutes them to an endosomal/recycling pathway. This is due to the Leu(683) and Cys(699) combination and another recycling motif (Gly(687)Thr(688)) that was previously identified in the hLHR. The importance of both motifs can be readily ascertained in the context of a murine delta opioid receptor/hLHR chimera. The importance of the Gly(687)Thr(688) motif is revealed mostly in the context of a rat LHR/hLHR chimera. These studies define a novel, noncontiguous, transferable motif that participates in the sorting of internalized GPCRs.