Structure and Activation Mechanism of the Visual Pigment Rhodopsin Rhodopsin is a specialized G protein-coupled receptor (GPCR) found in vertebrate rod cells. Absorption of light by its 11-cis retinal chromophore leads to rapid photochemical isomerization and receptor activation. Structural changes on the extracellular side of rhodopsin induced by the retinal isomerization are coupled to motion of the membrane-spanning helices to create a G-protein binding pocket on the intracellular side of the receptor. The existing crystal structures of rhodopsin provide a high-resolution framework to study in detail the role of specific residues and motifs in receptor activation. Because of the high conservation of many of the key residues involved activation of rhodopsin, the emerging model indicates that rather than being unique, the visual receptors provide a basis for understanding the common structural and dynamic elements in the class A GPCRs. The general experimental strategy is to use solid-state NMR spectroscopy in combination with mutational, optical and biochemical methods to target specific regions in the inactive and active states of the receptor. The goal is to understand in atomic detail the interplay between specific signature, group-conserved and subfamily-conserved motifs in the activation mechanism of rhodopsin and derive the basis of a working model for the activation of other GPCRs.
Three specific aims address structure-function questions involving regions on the extracellular side of the receptor (Aim 1), within the transmembrane (TM) core (Aim 2) and on the intracellular side of the receptor (Aim 3).
In Aim 1, we describe two hydrogen-bonding networks that tether extracellular loop 2 (EL2) to the ends of the TM helices H5-H7. We propose NMR measurements to quantify the displacement of EL2 upon activation and to establish how this displacement is coupled to helix motion.
In Aim 2, we target the conserved stable core of rhodopsin composed of interlocking signature and group-conserved residues. We hypothesize that H6 rotates in the conversion to Meta I and then tilts outward upon deprotonation of the retinal Schiff base and associated motion of EL2.
In Aim 3, we focus on the G-protein and its interactions with residues on the intracellular surface of Meta I and Meta II. The experiments target the structural transitions between inactive and active complexes of rhodopsin with G1 peptide or G-protein. In addition, our studies address how specific mutations lead to retinal diseases through constitutive activation, receptor misfolding or stabilization of non-functional receptor conformations.

Public Health Relevance

Structure and Activation Mechanism of the Visual Pigment Rhodopsin Rhodopsin is the visual receptor in the retina responsible for converting light into a chemical signal. Two diseases - autosomal dominant retinitis pigmentosa and congenital stationary night blindness - are associated with mutations in the receptor. The proposed research will uncover the mechanism for light- activation of rhodopsin and how specific mutations lead to rhodopsin-linked diseases. Rhodopsin is also a prototypical member of the family of class A G protein-coupled receptors, which are the largest target for current pharmaceuticals. The proposed studies will provide a framework for drug development within this large family of receptors.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM041412-21
Application #
8537202
Study Section
Biochemistry and Biophysics of Membranes Study Section (BBM)
Program Officer
Chin, Jean
Project Start
1988-12-01
Project End
2015-08-31
Budget Start
2013-09-01
Budget End
2014-08-31
Support Year
21
Fiscal Year
2013
Total Cost
$415,047
Indirect Cost
$113,797
Name
State University New York Stony Brook
Department
Biochemistry
Type
Schools of Medicine
DUNS #
804878247
City
Stony Brook
State
NY
Country
United States
Zip Code
11794
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Xu, Bing; Chakraborty, Raja; Eilers, Markus et al. (2013) High-level expression, purification and characterization of a constitutively active thromboxane A2 receptor polymorphic variant. PLoS One 8:e76481
Smith, Steven O (2012) Insights into the activation mechanism of the visual receptor rhodopsin. Biochem Soc Trans 40:389-93
Arakawa, Makoto; Chakraborty, Raja; Upadhyaya, Jasbir et al. (2011) Structural and functional roles of small group-conserved amino acids present on helix-H7 in the ýý(2)-adrenergic receptor. Biochim Biophys Acta 1808:1170-8
Goncalves, Joseph A; South, Kieron; Ahuja, Shivani et al. (2010) Highly conserved tyrosine stabilizes the active state of rhodopsin. Proc Natl Acad Sci U S A 107:19861-6
Smith, Steven O (2010) Structure and activation of the visual pigment rhodopsin. Annu Rev Biophys 39:309-28
Goncalves, Joseph A; Ahuja, Shivani; Erfani, Sina et al. (2010) Structure and function of G protein-coupled receptors using NMR spectroscopy. Prog Nucl Magn Reson Spectrosc 57:159-80
Hornak, Viktor; Ahuja, Shivani; Eilers, Markus et al. (2010) Light activation of rhodopsin: insights from molecular dynamics simulations guided by solid-state NMR distance restraints. J Mol Biol 396:510-27
Ahuja, Shivani; Eilers, Markus; Hirshfeld, Amiram et al. (2009) 6-s-cis Conformation and polar binding pocket of the retinal chromophore in the photoactivated state of rhodopsin. J Am Chem Soc 131:15160-9

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