C-terminal threonines and serines play distinct roles in the desensitization of rhodopsin, a G protein-coupled receptor
Anthony W Azevedo,
Thuy Doan,
Hormoz Moaven,
Iza Sokal,
Faiza Baameur,
Sergey A Vishnivetskiy,
Kristoff T Homan,
John JG Tesmer,
Vsevolod V Gurevich,
Jeannie Chen,
Fred Rieke
Affiliations
Anthony W Azevedo
Department of Physiology and Biophysics, University of Washington, Seattle, United States
Thuy Doan
Department of Ophthalmology, University of Washington, Seattle, United States
Hormoz Moaven
Departments of Cell & Neurobiology and Ophthalmology, Zilkha Neurogenetic Institute, Keck School of Medicine of University of Southern California, Los Angeles, United States
Iza Sokal
Department of Physiology and Biophysics, University of Washington, Seattle, United States
Faiza Baameur
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, United States
Sergey A Vishnivetskiy
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, United States
Kristoff T Homan
Life Sciences Institute, Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, United States
John JG Tesmer
Life Sciences Institute, Departments of Pharmacology and Biological Chemistry, University of Michigan, Ann Arbor, United States
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, United States
Jeannie Chen
Departments of Cell & Neurobiology and Ophthalmology, Zilkha Neurogenetic Institute, Keck School of Medicine of University of Southern California, Los Angeles, United States
Fred Rieke
Department of Physiology and Biophysics, University of Washington, Seattle, United States; Howard Hughes Medical Institute, University of Washington, Seattle, United States
Rod photoreceptors generate measurable responses to single-photon activation of individual molecules of the G protein-coupled receptor (GPCR), rhodopsin. Timely rhodopsin desensitization depends on phosphorylation and arrestin binding, which quenches G protein activation. Rhodopsin phosphorylation has been measured biochemically at C-terminal serine residues, suggesting that these residues are critical for producing fast, low-noise responses. The role of native threonine residues is unclear. We compared single-photon responses from rhodopsin lacking native serine or threonine phosphorylation sites. Contrary to expectation, serine-only rhodopsin generated prolonged step-like single-photon responses that terminated abruptly and randomly, whereas threonine-only rhodopsin generated responses that were only modestly slower than normal. We show that the step-like responses of serine-only rhodopsin reflect slow and stochastic arrestin binding. Thus, threonine sites play a privileged role in promoting timely arrestin binding and rhodopsin desensitization. Similar coordination of phosphorylation and arrestin binding may more generally permit tight control of the duration of GPCR activity.
