LIPID MODULATION OF RHODOPSIN SIGNALING IN MEMBRANES
Principal Investigator: Michael Brown
Abstract: DESCRIPTION (provided by applicant): Here we shall test the hypothesis that the retinal rod disk membrane lipid constituents govern visual function through their influences on signaling and amplification processes involving rhodopsin. Emphasis will be placed on the role of the membrane environment in modulating the Meta I-Meta II equilibrium, which is the signaling event in visual excitation. The retinal rod disk membranes are extraordinarily abundant in phospholipids containing highly polyunsaturated fatty acids, including docosahexaenoic acid (DHA;22:6-omega-3) and arachidonic acid (20:4-omega-6). Alterations of visual function are found to occur in essential fatty acid deficiency. Biophysical methods will characterize the influences of membrane lipids on the Meta I}Meta II transition of rhodopsin. Specific Aims are to apply a multidisciplinary approach to (1) identify the membrane lipids that function as agonists or antagonists of rhodopsin signaling;(2) elucidate the properties of membrane lipid bilayers that influence the photochemical function of rhodopsin;(3) illuminate the role of lipid polyunsaturation in rhodopsin activation;(4) discover how electrostatic properties of the membrane govern rhodopsin activation;and (5) establish how the membrane lipid influences on rhodopsin are amplified in visual signaling. A time-resolved multi-wavelength approach based on an optical multi-channel analyzer (OMA) will be used to study the kinetics and mechanism of rhodopsin activation. In addition, Fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET), and plasmon waveguide resonance (PWR) spectroscopy will elucidate the retinal environment, protein conformation, and oligomerization or association of rhodopsin in the dark, Meta I, and Meta II states. A new flexible surface model (FSM) will provide a framework for understanding how the signaling function of rhodopsin is driven by non-specific properties of the membrane phospholipids, including membrane lipid curvature and hydrophobic forces within the bilayer. The FSM describes the lipid-protein interactions in terms of a balance of the curvature deformation energy, due to elastic stress/strain of the bilayer, with the solvation energy of the proteolipid interface. An additional aspect entails the interplay of the bilayer electrostatics including the surface charge density and the electrical double layer with the above bilayer properties. The influences of polyunsaturated membrane phospholipids on later amplification stages of the visual photoresponse will be investigated, including the binding and activation of the G protein (transducin) to photolyzed rhodopsin, and subsequent activation of cGMP phosphodiesterase. In this manner, a truly comprehensive picture of the triggering and amplification steps of the visual process will be provided at the membrane level in relation to dietary investigations of essential ?3 fatty acid deficiency in humans. PUBLIC HEALTH RELEVANCE: The proposed research will investigate the molecular basis for essential fatty acid deficiency in the retina, which is part of the brain and comprises a uniquely accessible model for the mammalian nervous system. Current knowledge indicates that long chain polyunsaturated fatty acids derived from essential ?3 fatty acids play an important role in retinal and brain development involving human infants. Moreover, polyunsaturated lipids are involved in diseases such as Parkinson's disease, cardiovascular disease, cancer, aging, and other physiological and pathological anomalies. The proposed in vitro studies of the influence of the membrane lipid bilayer on rhodopsin activity will test a specific framework for explaining the effects of essential fatty acid) deficiency in the visual system at the membrane level. This work is pertinent to the role of polyunsaturated lipids in the function and dysfunction of central nervous system of humans with attendant insights that may be of eventual therapeutic benefit.
Funding Period: ----------------2008 - ---------------2011-
more information: NIH RePORT
- Bolalipid membrane structure revealed by solid-state 2H NMR spectroscopyDavid P Holland
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
J Am Chem Soc 130:4584-5. 2008..The approximate hydrophobic layer thickness and area per lipid are 18.4 A and 60.4 A2, respectively, at 25 degrees C, and their respective thermal expansion coefficients are within 20% of the monopolar phospholipid, DLPC...
- Retinal ligand mobility explains internal hydration and reconciles active rhodopsin structuresNicholas Leioatts
Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, United States
Biochemistry 53:376-85. 2014..48) residue. In addition, enhanced ligand flexibility upon light activation provides an explanation for the different retinal orientations observed in X-ray crystal structures of active rhodopsin. ..
- High-resolution NMR reveals secondary structure and folding of amino acid transporter from outer chloroplast membraneJames D Zook
Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, United States of America
PLoS ONE 8:e78116. 2013..The results provide the necessary basis for high-resolution structural determination of this important plant membrane protein. ..
- Retinal conformation governs pKa of protonated Schiff base in rhodopsin activationShengshuang Zhu
Department of Chemistry, Wabash College, Crawfordsville, Indiana 47933, United States
J Am Chem Soc 135:9391-8. 2013..These new results shed light on important mechanistic aspects of retinal conformational changes that are involved in the activation of rhodopsin in the visual process. ..
- Curvature forces in membrane lipid-protein interactionsMichael F Brown
Department of Chemistry and Biochemistry and Department of Physics, University of Arizona, Tucson, AZ 85721, USA
Biochemistry 51:9782-95. 2012..An increased awareness of curvature forces suggests that research will accelerate as structural biology becomes more closely entwined with the physical chemistry of lipids in explaining membrane structure and function...
- Two protonation switches control rhodopsin activation in membranesMohana Mahalingam
Biophysics Section, Institute of Molecular Medicine and Cell Research, Albert Ludwigs University, Hermann Herder Strasse 9, D 79104 Freiburg, Germany
Proc Natl Acad Sci U S A 105:17795-800. 2008..In light of the conservation of the E(D)RY motif in rhodopsin-like GPCRs, protonation of this carboxylate also may serve a similar function in signal transduction of other members of this receptor family...
- Raftlike mixtures of sphingomyelin and cholesterol investigated by solid-state 2H NMR spectroscopyTim Bartels
Laboratory of Neurodegenerative Disease Research, Ludwig Maximilian University, 80336 Munich, Germany
J Am Chem Soc 130:14521-32. 2008..Hydrophobic matching explains the occurrence of raftlike domains in cellular membranes at intermediate cholesterol concentrations but not saturating amounts of cholesterol...
- Reconstitution of rhodopsin into polymerizable planar supported lipid bilayers: influence of dienoyl monomer structure on photoactivationVaruni Subramaniam
Department of Chemistry, University of Arizona, Tucson, Arizona 85721 0041, USA
Langmuir 24:11067-75. 2008..These results should provide guidance for the design of robust lipid bilayers functionalized with transmembrane proteins for use in membrane-based biochips and biosensors...
- Fluid mechanical matching of H+-ATP synthase subunit c-ring with lipid membranes revealed by 2H solid-state NMRMasatoshi Kobayashi
Institute for Protein Research, Osaka University, Yamadoaka, Suita 565 0871, Japan
Biophys J 94:4339-47. 2008..These findings may be important for the torque generation in the rotary catalytic mechanism of the F(1)F(o)-ATPse molecular motor...
- Retinal conformation and dynamics in activation of rhodopsin illuminated by solid-state H NMR spectroscopyMichael F Brown
Department of Chemistry, University of Arizona, Tucson, AZ, USA
Photochem Photobiol 85:442-53. 2009..Solid-state (2)H NMR thus provides information about the flow of energy that triggers changes in hydrogen-bonding networks and helix movements in the activation mechanism of the photoreceptor...
- FTIR analysis of GPCR activation using azido probesShixin Ye
Laboratory of Molecular Biology and Biochemistry, The Rockefeller University, New York, New York, USA
Nat Chem Biol 5:397-9. 2009..We used FTIR difference spectroscopy to monitor the azido probe and show that the electrostatic environments of specific interhelical networks change during receptor activation...
- Retinal dynamics during light activation of rhodopsin revealed by solid-state NMR spectroscopyMichael F Brown
Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA Department of Physics, University of Arizona, Tucson, AZ 85721, USA
Biochim Biophys Acta 1798:177-93. 2010..The solid-state (2)H NMR data are discussed with regard to the pathway of the energy flow in the receptor activation mechanism...
- Phase separation in binary mixtures of bipolar and monopolar lipid dispersions revealed by 2H NMR spectroscopy, small angle x-ray scattering, and molecular theoryDavid P Brownholland
Department of Chemistry, Purdue University, West Lafayette, Indiana, USA
Biophys J 97:2700-9. 2009..These observations are consistent with the presence of microphase-separated domains in the mixed membrane samples that arise from POPC-C(20)BAS hydrophobic mismatch...
- Sequential rearrangement of interhelical networks upon rhodopsin activation in membranes: the Meta II(a) conformational substateEkaterina Zaitseva
Biophysics Section, Institute of Molecular Medicine and Cell Research, University of Freiburg, Hermann Herder Str 9, D 79104 Freiburg, Germany
J Am Chem Soc 132:4815-21. 2010....
- Solid-state ²H NMR shows equivalence of dehydration and osmotic pressures in lipid membrane deformationK J Mallikarjunaiah
Department of Chemistry, University of Arizona, Tucson, Arizona, USA
Biophys J 100:98-107. 2011..This research demonstrates the applicability of solid-state ²H NMR spectroscopy together with bilayer stress techniques for investigating the mechanism of pressure sensitivity of membrane proteins...
- Retinal dynamics underlie its switch from inverse agonist to agonist during rhodopsin activationAndrey V Struts
Department of Chemistry, University of Arizona, Tucson, AZ, USA
Nat Struct Mol Biol 18:392-4. 2011..We propose a multiscale activation mechanism whereby retinal initiates collective helix fluctuations in the meta I-meta II equilibrium on the microsecond-to-millisecond timescale...
- Steric and electronic influences on the torsional energy landscape of retinalBlake Mertz
Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA
Biophys J 101:L17-9. 2011..These results are highly relevant for the parameterization of molecular mechanics force fields which form the basis of molecular dynamics simulations of retinal proteins such as rhodopsin...
- Molecular simulations and solid-state NMR investigate dynamical structure in rhodopsin activationBlake Mertz
Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
Biochim Biophys Acta 1818:241-51. 2012..This article is part of a Special Issue entitled: Membrane protein structure and function...
- Molecular dynamics simulations reveal specific interactions of post-translational palmitoyl modifications with rhodopsin in membranesBjoern E S Olausson
Institute of Pharmacy, Martin Luther University Halle Wittenberg, D 06120 Halle Saale, Germany
J Am Chem Soc 134:4324-31. 2012....