PHOTOTRANSDUCTION IN HEALTH AND DISEASE

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Abstract Phototransduction is a fundamental biological process involving a set of biochemical reactions in photoreceptor cells initiating vision. The long-term goal of this research program is to understand the molecular mechanisms underlying the biochemical events in phototransduction under normal and diseased states. Rhodopsin and cone opsins are the light receptors in photoreceptors cells that initiate vision upon stimulation by light. The primary focus here is on rhodopsin structure, function and dysfunction. Rhodopsin plays a central role in phototransduction as the initiator of signaling and also plays an important role in maintaining the health of photoreceptor cells. The rhodopsin gene is a hot spot for mutations causing inherited retinal diseases such as retinitis pigmentosa (RP) and congenital stationary night blindness (CSNB), which currently have no cure or effective treatment. Rhodopsin is a prototypical G protein-coupled receptor and therefore findings here can provide insights on other members of this superfamily of proteins that share commonalities in structure and mechanisms of action. Despite the wealth of knowledge available for rhodopsin, gaps in our structural and molecular understanding of the receptor still exist and a mechanistic description on the effect of mutations in the light receptor causing vision disorders is incomplete. Less is known about the structure, function, and dysfunction of cone opsins, a secondary focus here in one aim. Three aspects of rhodopsin structure and function will be examined in this proposal. Opsins must adopt a proper three-dimensional structure for proper function in photoreceptor cells. In aim 1, the misfolding and aggregation of a set of mutants that cause RP and a mutant in a cone opsin causing blue cone monochromacy will be characterized, and the resulting consequences in the retina of mouse models examined. Rhodopsin forms a supramolecular structure at its site of action in the rod outer segment of photoreceptor cells to carry out its function under scotopic conditions. In aim 2, the dynamics of this supramolecular structure will be visualized and the impact of diseased states on this membrane organization will be examined. The structure of rhodopsin is finely tuned to prevent activation of the receptor in the absence of light stimulation. Constitutive activity of rhodopsin can lead to a variety of phenotypes causing CSNB or RP. In aim 3, the molecular origin of the different phenotypes caused by mutations causing constitutive activity in rhodopsin will be examined. The proposal combines the study of a variety of genetically modified mice with innovative biophysical and biochemical methods to answer questions raised in each aim. Results from our studies will lead to a more accurate mechanistic framework to understand the function of the system under normal conditions and dysfunctions in inherited retinal diseases, which will provide new avenues for scientific inquiry. The long-term impact in studying fundamental aspects of rhodopsin structure and function will be the potential for targeted therapeutics and discovery of novel drug targets.