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Future directions for rhodopsin structure and function studies

Hargrave, Paul A. (1995) Future directions for rhodopsin structure and function studies.

Short Abstract:

To understand how the photoreceptor protein rhodopsin performs its role as a receptor, its structure needs to be determined at the atomic level. Upon receiving a photon of light, rhodopsin undergoes a change in conformation that allows it to bind and activate the G-protein, transducin. An important future goal should be to determine the structure both of the inactive state of rhodopsin and of the photoactivated state, R*. This should provide the groundwork necessary to perform experiments to determine how rhodopsin achieves its signalling state R* and how R* functions to activate transducin. To do this, the crystal structure of both rhodopsin and R* must be determined. Few membrane proteins have been successfully crystallized so this is not a trivial undertaking. Two-dimensional and/or three-dimensional crystals of rhodopsin must be prepared that are well-ordered, to produce a high-resolution structure. Rhodopsin must be purified to homogeneity and the appropriate detergent(s) selected for crystallization experiments. Long-term thermal stability of the rhodopsin/detergent complex must be achieved in presence of a precipitant. Two-dimensional crystals may offer advantages in investigating the structure of R*, but the structure obtained may be limited in resolution. It is necessary to work with rhodopsin in the dark unless suitable light-stable retinal derivatives are developed. Protein engineering of rhodopsin offers attractive opportunities to improve its ability to crystallize, but is presently hindered by lack of a high-yielding expression system. Knowledge of the structure of rhodopsin will be of general significance. Since rhodopsin is a member of the family of G-protein-coupled receptors, knowledge of the structure and mechanism of action of rhodopsin suggests by analogy how other members of the receptor family may function.

Long Abstract:

To understand how the photoreceptor protein rhodopsin performs its role as a receptor, its structure needs to be determined at the atomic level. Upon receiving a photon of light, rhodopsin undergoes a change in conformation that allows it to bind and activate the G-protein, transducin. An important future goal should be to determine the structure both of the inactive state of rhodopsin and of the photoactivated state, R*. This should provide the groundwork necessary to perform experiments to determine how rhodopsin achieves its signalling state R* and how R* functions to activate transducin. To do this, the crystal structure of both rhodopsin and R* must be determined. Few membrane proteins have been successfully crystallized so this is not a trivial undertaking. Two-dimensional and/or three-dimensional crystals of rhodopsin must be prepared that are well-ordered, to produce a high-resolution structure. Rhodopsin must be purified to homogeneity and the appropriate detergent(s) selected for crystallization experiments. Long-term thermal stability of the rhodopsin/detergent complex must be achieved in presence of a precipitant. Two-dimensional crystals may offer advantages in investigating the structure of R*, but the structure obtained may be limited in resolution. It is necessary to work with rhodopsin in the dark unless suitable light-stable retinal derivatives are developed. Protein engineering of rhodopsin offers attractive opportunities to improve its ability to crystallize, but is presently hindered by lack of a high-yielding expression system. Knowledge of the structure of rhodopsin will be of general significance. Since rhodopsin is a member of the family of G-protein-coupled receptors, knowledge of the structure and mechanism of action of rhodopsin suggests by analogy how other members of the receptor family may function.

Keywords:	Rhodopsin, X-ray structure, photoreceptor, G- protein coupled receptor, protein structure, retinal, membrane protein, protein crystallization, membrane protein crystallization, detergent
Subjects:	BBS Special Issues: Controversies in Neuroscience: III - Signal Transduction in the Retina and Brain Neuroscience: Neuroanatomy Neuroscience: Neurochemistry Neuroscience: Neurology Neuroscience: Neurophysiology Neuroscience: Neuropsychology Psychology: Perceptual Cognitive Psychology
ID code:	bbs00000549
Deposited by:	Paul A Hargrave on 02 May 2001