G Protein-Coupled Receptors Regulation by Acylation

Several G protein-coupled receptors (GPCRs) are modified posttranslationally by acylation, including the 5-hydroxytryptamine receptor (5-HT_4a), and this modification has different effects on receptor function, depending on the receptor. Ponimaskin et al. used a heterologous expression system with the wild-type and various cysteine mutants to show that the 5-HT_4a receptor is palmitoylated on at least three cysteine residues in the COOH-terminal domain. The palmitoylation is dynamic, and turnover of the acyl group can be stimulated by agonists of the receptor. Analysis of the coupling of the receptor to the Gα_s subunit showed that if the membrane proximal cysteines (Cys³²⁸ and Cys³²⁹) were mutated to prevent palmitoylation, the receptor exhibited enhanced constitutive coupling to the G protein. Application of agonist to cells expressing this cysteine-mutated receptor increased guanosine 5'-O-(3-thiotriphosphate) (GTP--S) loading of the G protein, but the difference between the stimulated receptor and the unliganded receptor was smaller than the difference for the stimulated and resting wild-type receptor. Two additional assays showed that the Cys³²⁸ and Cys³²⁹ mutants exhibited higher constitutive activity for stimulating downstream signaling events. The pharmacological profile of the Cys³²⁸ and Cys³²⁹ mutant showed that this receptor had a higher affinity for serotonin than did the native receptor. These data all point to a role for dynamic and regulated palmitoylation in controlling receptor conformation, leading to changes in receptor ligand affinity and constitutive receptor activity for the 5-HT_4a receptor.

E. G. Ponimaskin, M. Heine, L. Joubert, M. Sebben, U. Bickmeyer, D. W. Richter, A. Dumuis, The 5-hydroxytryptamine (4a) receptor is palmitoylated at two different sites, and acylation is critically involved in regulation of receptor constitutive activity. J. Biol. Chem. 277, 2534-2546 (2002). [Abstract] [Full Text]