Yanagawa, M. | bioRxiv Science

bioRxiv2017

Lipid-protein interplay in dimerization of the juxtamembrane domains of epidermal growth factor receptor

Transmembrane (TM) helix and juxtamembrane (JM) domains (TM-JM) bridge the extracellular and intracellular domains of single-pass membrane proteins, including epidermal growth factor receptor (EGFR). TM-JM dimerization plays a crucial role in regulation of EGFR kinase activity at the cytoplasmic side. Although the interaction of JM with membrane lipids is thought to be important to turn on EGF signaling and phosphorylation of Thr654 on JM leads to desensitization, the underlying kinetic mechanisms remain unclear. Especially, how Thr654 phosphorylation regulates EGFR activity is largely unknown. Here, combining single-pair FRET imaging and nanodisc techniques, we showed that phosphatidylinositol 4,5-bis phosphate (PIP2) facilitated JM dimerization effectively. We also found that Thr654 phosphorylation dissociated JM dimers in the membranes containing acidic lipids, suggesting that Thr654 phosphorylation electrostatically prevented the interaction with basic residues in JM and acidic lipids. Based on the single-molecule experiment, we clarified the kinetic pathways of monomer (inactive state) - dimer (active state) transition of JM domains and alteration in the pathways depending on the membrane lipid species and Thr654 phosphorylation.

biophysics↗

bioRxiv2017

Single-molecule diffusion-based estimation of GPCR activity

G 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.\n\nOne Sentence Summary: Single-molecule imaging for evaluating ligand effects on GPCRs by monitoring the diffusion dynamics on the cell surface.

biophysics↗