title: Constitutive phospholipid scramblase activity of a G protein-coupled receptor.
abstract: Opsin, the rhodopsin apoprotein, was recently shown to be an ATP-independent flippase (or scramblase) that equilibrates phospholipids across photoreceptor disc membranes in mammalian retina, a process required for disc homoeostasis. Here we show that scrambling is a constitutive activity of rhodopsin, distinct from its light-sensing function. Upon reconstitution into vesicles, discrete conformational states of the protein (rhodopsin, a metarhodopsin II-mimic, and two forms of opsin) facilitated rapid (>10,000 phospholipids per protein per second) scrambling of phospholipid probes. Our results indicate that the large conformational changes involved in converting rhodopsin to metarhodopsin II are not required for scrambling, and that the lipid translocation pathway either lies near the protein surface or involves membrane packing defects in the vicinity of the protein. In addition, we demonstrate that β2-adrenergic and adenosine A2A receptors scramble lipids, suggesting that rhodopsin-like G protein-coupled receptors may play an unexpected moonlighting role in re-modelling cell membranes.
authors.affiliation: Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Goren
authors.affiliation: Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Takefumi
authors.initials: T
authors.lastname: Morizumi
authors.affiliation: Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA.
authors.forename: Indu
authors.initials: I
authors.lastname: Menon
authors.affiliation: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Jeremiah S
authors.initials: JS
authors.lastname: Joseph
authors.affiliation: Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA.
authors.forename: Jeremy S
authors.initials: JS
authors.lastname: Dittman
authors.affiliation: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Vadim
authors.initials: V
authors.lastname: Cherezov
authors.affiliation: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Stevens
authors.affiliation: 1] Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8 [2] Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Oliver P
authors.initials: OP
authors.lastname: Ernst
authors.affiliation: Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, USA.
authors.forename: Anant K
authors.initials: AK
authors.lastname: Menon
mesh_terms: D000818:Animals; D002417:Cattle; D055355:Opsins / Q000502:physiology; D049294:Phospholipid Transfer Proteins / Q000502:physiology*; D011487:Protein Conformation; D043683:Receptors, Adenosine A2 / Q000502:physiology; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D012243:Rhodopsin / Q000502:physiology*
chemical_list: D055355:Opsins; D049294:Phospholipid Transfer Proteins; D043683:Receptors, Adenosine A2; D018343:Receptors, Adrenergic, beta-2; D012243:Rhodopsin