Posttranslational Regulation of G Protein-Coupled Receptors

The G protein-coupled receptors (GPCRs) are a superfamily of transmembrane receptors that �structurally possess an extracellular amino terminus, seven transmembrane domains linked by extracellular and intracellular loops, and a cytoplasmic carboxyl terminus. They are synthesized by ribosomes and enter into the endoplasmic reticulum (ER), from which they are transported to Golgi apparatus and the trans-Golgi network (TGN) and finally move to the plasma membrane. At the plasma membrane, GPCRs receive environmental stimuli and relay the message to the cells. During these processes, GPCRs undergo posttranslational modifications that regulate their maturation, their function at the cell surface and even the ultimate fate of the internalized receptor after agonist treatment. There are four major types of posttranslational modifications – glycosylation, phosphorylation, palmitoylation, and ubiquitination, each of which has distinct roles in expression and function of GPCRs. In this �chapter we discuss the methods to study these posttranslational modifications and the findings of posttranslational modifications and their functional consequences on GPCRs, using opioid receptors as the main examples. Moreover, the detailed steps of the main methods are depicted and also our thoughts on future directions of this avenue of research.