Probing novel GPCR interactions using a combination of FRET and TIRF

Abstract

Recent work on G-protein coupled receptors (GPCRs) has highlighted the importance of homo- and heterodimerization in all areas of GPCR function, including trafficking, signaling and desensitization. Novel GPCR dimers and even high-order oligomers are constantly being discovered. Advances in techniques such as fluorescent microscopy have improved our ability to detect these interactions. As GPCRs represent the largest class of transmembrane signaling molecules in biology, these new insights into their function could vastly improve our understanding of the complex physiological role GPCRs play in cellular signaling. Utilizing a combination of classic biochemical approaches and newer techniques such as fluorescence resonance energy transfer (FRET) and total internal reflection fluorescence microscopy (TIRF), we recently demonstrated a novel interaction between M(2) muscarinic receptors and GABA(B) receptors. In this addendum, we address technical aspects of combining FRET and TIRF to study GPCR interactions and further discuss the physiological implications of the M(2)-GABA(B) heterodimer.

Keywords: FRET; GABAB; GPCR; TIRF; cAMP; dimerization; potassium channel.

Figure 1

FRET in epifluorescence vs. TIRF. (A) A cell illuminated by direct epifluorescence. Y—YFP flourophore; C—CFP fluorophore. Shaded blue areas represent regions illuminated by laser light. In epifluorescence, fluorophores throughout the whole cell, including intracellular compartments, are illuminated. (B) The same cell illuminated under TIRF, where θ represents the critical angle. Only flourophores within ∼100 nm of the plasma membrane are illuminated.