A Constitutively Activating Mutation Alters the Dynamics and Energetics of a Key Conformational Change in a Ligand-free G Protein-coupled Receptor

• Published in: The Journal of biological chemistry Vol. 288; no. 39; pp. 28207 - 28216
• Main Authors: Tsukamoto, Hisao, Farrens, David L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 27.09.2013; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Cattle; Chlorocebus aethiops; Conformational Transitions; COS Cells; Crystallography, X-Ray; Detergents - chemistry; Energy Landscapes; Fluorescence; G Protein-coupled Receptors (GPCR); Ligands; Lipids - chemistry; Micelles; Molecular Biophysics; Mutation; Opsins - chemistry; Opsins - genetics; Protein Dynamics; Protein Energetics; Protein Structure, Secondary; Receptor Structure-Function; Receptors, G-Protein-Coupled - chemistry; Receptors, G-Protein-Coupled - genetics; Rhodopsin; Rhodopsin - chemistry; Rhodopsin - genetics; Site-directed Fluorescence Labeling (SDFL); Spectrometry, Fluorescence; Tryptophan - chemistry; Tryptophan-induced Quenching (TrIQ); G Protein-coupled Receptors (GPCR); Receptor Structure-Function; Rhodopsin; Site-directed Fluorescence Labeling (SDFL); Protein Dynamics; Conformational Transitions; Fluorescence; Energy Landscapes; Tryptophan-induced Quenching (TrIQ); Protein Energetics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.472464

G protein-coupled receptors (GPCRs) undergo dynamic transitions between active and inactive conformations. Usually, these conversions are triggered when the receptor detects an external signal, but some so-called constitutively activating mutations, or CAMs, induce a GPCR to bind and activate G proteins in the absence of external stimulation, in ways still not fully understood. Here, we investigated how a CAM alters the structure of a GPCR and the dynamics involved as the receptor transitions between different conformations. Our approach used site-directed fluorescence labeling (SDFL) spectroscopy to compare opsin, the ligand-free form of the GPCR rhodopsin, with opsin containing the CAM M257Y, focusing specifically on key movements that occur in the sixth transmembrane helix (TM6) during GPCR activation. The site-directed fluorescence labeling data indicate opsin is constrained to an inactive conformation both in detergent micelles and lipid membranes, but when it contains the M257Y CAM, opsin is more dynamic and can interact with a G protein mimetic. Further study of these receptors using tryptophan-induced quenching (TrIQ) methods indicates that in detergent, the CAM significantly increases the population of receptors in the active state, but not in lipids. Subsequent Arrhenius analysis of the TrIQ data suggests that, both in detergent and lipids, the CAM lowers the energy barrier for TM6 movement, a key transition required for conversion between the inactive and active conformations. Together, these data suggest that the lowered energy barrier is a primary effect of the CAM on the receptor dynamics and energetics. Background: Constitutively active mutations (CAMs) affect the dynamics of G protein-coupled receptors (GPCRs), through undefined mechanisms. Results: Site-directed fluorescence labeling (SDFL) studies find a CAM (M257Y) alters the dynamics of the GPCR ligand-free opsin. Conclusion: The M257Y CAM alters the dynamics of the conversion between active and inactive opsin conformations. Significance: SDFL can be used to gain insights into how CAMs affect the dynamics of G protein-coupled receptors.