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
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]
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
A dark and constitutively
active mutant of the tiger salamander UV pigment. Kono M, Crouch RK, Oprian DD. (2005) Biochemistry.
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.
Opsin activation as a cause of
congenital night blindness. Jin S, Cornwall MC, Oprian DD. (2003) Nat Neurosci. 6:731-5.
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.
Slow binding of retinal to
rhodopsin mutants G90D and T94D. Gross AK, Xie G, Oprian DD. (2003) Biochemistry. 42:2002-8.
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
Last update: July 8, 2009