Faculty Opinions recommendation of Single-molecule analysis of fluorescently labeled G-protein-coupled receptors reveals complexes with distinct dynamics and organization.

G-protein-coupled receptors (GPCRs) constitute the largest family of integral membrane proteins in the human genome and are responsible for various important signaling pathways for vision, olfaction, gustation, emotion, cell migration, etc. A distinct feature of the GPCR-family proteins is that many GPCRs, including the prototypical GPCR, β2-adrenergic receptor (β2AR), elicit low levels of basal constitutive signals without agonist stimulation, which function in normal development and various diseases1–3. However, how the basal signals are induced is hardly known. Another general distinctive feature of GPCRs is to form metastable homo-dimers, with lifetimes on the order of 0.1 s, even in the resting state. Here, our single-molecule-based quantification4 determined the dissociation constant of β2AR homo-dimers in the PM (1.6 ± 0.29 copies/μm2) and their lifetimes (83.2 ± 6.4 ms), and furthermore found that, in the resting state, trimeric G-proteins were recruited to both β2AR monomers and homo-dimers. Importantly, inverse agonists, which suppress the GPCR’s basal constitutive activity, specifically blocked the G-protein recruitment to GPCR homo-dimers, without affecting that to monomers. These results indicate that the G-proteins recruited to transient GPCR homo-dimers are responsible for inducing their basic constitutive signals. These results suggest novel drug development strategies to enhance or suppress GPCR homo-dimer formation.

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Title: Single-molecule diffusion-based estimation of ligand effects on G protein-coupled receptors

10.1101/205161 ◽

2017 ◽

Author(s):

Masataka Yanagawa ◽

Michio Hiroshima ◽

Yuichi Togashi ◽

Mitsuhiro Abe ◽

Takahiro Yamashita ◽

...

Keyword(s):

Diffusion Coefficient ◽

Cell Surface ◽

G Protein ◽

Single Molecule ◽

G Protein Coupled Receptors ◽

Single Molecule Imaging ◽

Imaging Analysis ◽

Coated Pits ◽

Ligand Effects ◽

G Protein Coupled

AbstractG protein-coupled receptors (GPCRs) are major drug targets and have high potential for drug discovery. The development of a method for measuring the activities of GPCRs is essential for pharmacology and drug screening. However, it is difficult to measure the effects of a drug by monitoring the receptor on the cell surface, and changes in the concentrations of downstream signaling molecules, which depend on signaling pathway selectivity of the receptor, are used as an index of the receptor activity. Here, we show that single-molecule imaging analysis provides an alternative method for assessing ligand effects on GPCR. We monitored the dynamics of the diffusion of metabotropic glutamate receptor 3 (mGluR3), a class C GPCR, under various ligand conditions by using total internal reflection fluorescence microscopy (TIRFM). The single-molecule tracking analysis demonstrates that changes in the average diffusion coefficient of mGluR3 quantitatively reflect the ligand-dependent activity. Then, we reveal that the diffusion of receptor molecules is altered by the common physiological events associated with GPCRs, including G protein binding or accumulation in clathrin-coated pits, by inhibition experiments and dual-color single-molecule imaging analysis. We also confirm the generality of agonist-induced diffusion change in class A and B GPCRs, demonstrating that the diffusion coefficient is a good index for estimating the ligand effects on many GPCRs regardless of the phylogenetic groups, chemical properties of the ligands, and G protein-coupling selectivity.One Sentence Summary: Single-molecule imaging for evaluating ligand effects on GPCRs by monitoring the diffusion dynamics on the cell surface.

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