Our laboratory is interested in the structure and function of G protein-coupled receptors with particular focus on the subgroup of receptors known as visual pigments. The pigments are major components of rod and cone photoreceptor cells and form the basis of phototransduction in the vertebrate retina. As is typical of G protein-coupled receptors, the visual pigments are integral membrane proteins composed of seven transmembrane helical segments. However, what is atypical is that each pigment is bound covalently to a small molecule ligand, 11-cis-retinal, which is a chromophore for the absorption of light.

Spectral Tuning: There are four visual pigments in the human retina: rhodopsin, the pigment of rod photoreceptor cells, and the blue, green and red color vision pigments of cone photoreceptor cells. These four pigments have absorption spectra which span (actually define) the visible region of the electromagnetic spectrum. And yet, the small molecule chromophore responsible for absorption of light is the same in each pigment. One of the goals of our research is to understand the underlying mechanism by which the spectrum of each pigment is “tuned” by interactions of the retinal chromophore with amino acid side chains in the active site of the proteins.

Mechanism of Retinal Disease: A large number of mutations in rhodopsin are known to cause inherited diseases of the retina. We are interested in a small group of these which result in constitutive activation of rhodopsin - that is, these mutations cause the protein to activate the G protein transducin in the absence of light. The activating mutations are known to cause two different diseases: a devastating degenerative disease of the retina known as retinitis pigmentosa and, in comparison, a relatively benign disease known as congenital stationary night blindness. Our goal is to elucidate the underlying molecular mechanisms responsible for pathophysiology in these diseases. To do this, we employ a broad array of techniques ranging from classical biochemistry and mutagenesis for in vitro characterization of the mutant proteins to the development of transgenic animals combined with single-cell electrophysiology to test models of disease under in vivo conditions.

Structure of the Active State: Rhodopsin is the only G protein-coupled receptor for which a structure has been determined by x-ray crystallography. While the structure of rhodopsin has had an enormous impact on our understanding of the protein it is clear that we are at the very beginning of these structural studies and major questions remain. In particular, we still do not have a structure for the active conformation of the protein – the published rhodopsin structure is for the inactive- or dark-state. Our laboratory is currently undertaking a major effort to determine the x-ray crystal structure of the active state of rhodopsin. In addition, we are undertaking efforts to determine the crystal structure of other G protein-coupled receptors.

Selected Recent Publications:

Crystal structure of a thermally stable rhodopsin mutant. Standfuss J, Xie G, Edwards PC, Burghammer M, Oprian DD, Schertler GF. J Mol Biol. 2007 Oct 5;372(5):1179-88. [abstract]

Transducin activation by nanoscale lipid bilayers containing one and two rhodopsins. Bayburt TH, Leitz AJ, Xie G, Oprian DD, Sligar SG. J Biol Chem. 2007 May 18;282(20):14875-81. [abstract]

Stable rhodopsin/arrestin complex leads to retinal degeneration in a transgenic mouse model of autosomal dominant retinitis pigmentosa. Chen J, Shi G, Concepcion FA, Xie G, Oprian D, Chen J. J Neurosci. 2006 Nov 15;26(46):11929-37. [abstract]

Recoverin binds exclusively to an amphipathic peptide at the N terminus of rhodopsin kinase, inhibiting rhodopsin phosphorylation without affecting catalytic activity of the kinase. Higgins MK, Oprian DD, Schertler GF. (2006) J Biol Chem. 2006 Jul 14;281(28):19426-32. Epub 2006 May 4. [abstract]

Mislocalized rhodopsin does not require activation to cause retinal degeneration and neurite outgrowth in Xenopus laevis.Tam BM, Xie G, Oprian DD, Moritz OL. (2006) J Neurosci. 2006 Jan 4;26(1):203-9. [abstract]

A dark and constitutively active mutant of the tiger salamander UV pigment. Kono M, Crouch RK, Oprian DD. (2005) Biochemistry. 44:799-804. [abstract]

Structural origins of constitutive activation in rhodopsin: Role of the K296/E113 salt bridge. Kim JM, Altenbach C, Kono M, Oprian DD, Hubbell WL, Khorana HG. ( 2004) Proc Natl Acad Sci U S A. 101(34):12508-13. [abstract]

Role of the 9-methyl group of retinal in cone visual pigments. Das J, Crouch RK, Ma JX, Oprian DD, Kono M. (2004) Biochemistry. 43(18):5532-8. [abstract]

Opsin activation as a cause of congenital night blindness. Jin S, Cornwall MC, Oprian DD. (2003) Nat Neurosci. 6:731-5. [abstract]

An improved rhodopsin/EGFP fusion protein for use in the generation of transgenic Xenopus laevis. Jin S, McKee TD, Oprian DD. (2003) FEBS Lett. 542(1-3):142-6. [abstract]

Phototaxis, chemotaxis and the missing link. Oprian DD. (2003) Trends Biochem Sci. 28:167-9. [abstract]

Characterization of rhodopsin congenital night blindness mutant T94I. Gross AK, Rao VR, Oprian DD. (2003) Biochemistry. 42:2009-15. [abstract]

Slow binding of retinal to rhodopsin mutants G90D and T94D. Gross AK, Xie G, Oprian DD. (2003) Biochemistry. 42:2002-8. [abstract]

An opsin mutant with increased thermal stability. Xie G, Gross AK, Oprian DD. (2003) Biochemistry. 42:1995-2001. [abstract]

View Complete Publication List on PubMed: Daniel Oprian

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Last update: July 8, 2009