Isolation of Lipid Rafts by the Detergent-Based and Non-detergent-Based Methods for Localization of GPCRs with Immunoblotting and Laser Scanning Confocal Microscopy

The understanding of how biological membranes are organized and how they function has constantly been evolving over the past decades. Instead of just serving as a medium in which specific proteins are located, certain parts of the lipid bilayer contribute to platforms that assemble signaling complexes by providing a microenvironment that facilitates effective protein-protein interactions. G protein-coupled receptors (GPCRs) and relevant signaling molecules, including the heterotrimeric G proteins, key enzymes such as kinases and phosphatases, trafficking proteins, and secondary messengers, preferentially partition to these highly organized cell membrane microdomains, called lipid rafts. Lipid rafts are essential for the trafficking and signaling of GPCRs. The study of GPCR biology in the context of lipid rafts involves the localization of the GPCR of interest in lipid rafts, at the basal state and upon receptor agonism, and the evaluation of the biological functions of the GPCR in appropriate cell lines. The lack of standardized methodologies to study lipid rafts, in general, and of the workings of GPCRs in lipid rafts, in particular, and the inescapable drawbacks of current methods have hampered the complete understanding of the underlying molecular mechanisms. Newer methodologies that allow the study of GPCRs in their native form are needed. The use of complementary approaches that produce mutually supportive results appears to be the best way for drawing conclusions with regard to the distribution and activity of GPCRs in lipid rafts.