PhD Exit Seminar -Nihar Bhattacharya-Tuesday, August 7, 2018

PhD Exit Seminar

Tuesday, August 7, 2018 at 9:30am, Ramsay Wright Building, Room 432

Nihar Bhattacharya (Chang Lab)

“CHARACTERIZING VERTEBRATE RHODOPSIN NATURAL VARIATION IN EVOLUTION, FUNCTION, AND DISEASE”

Abstract

Vertebrate dim light vision is mediated by the rod visual pigment, rhodopsin, a member of the G protein-coupled receptor (GPCR) superfamily of proteins. In the dark, rhodopsin is covalently bound to a vitamin A-derived 11-cis chromophore, which acts as an inverse agonist to stabilize the inactive state of rhodopsin. When exposed to light of a maximal wavelength (λmax), the 11-cis retinal chromophore isomerizes to an all-trans conformation, initiating a series of structural shifts to the light-activated state of rhodopsin. This results in a signalling cascade within the rod photoreceptor cell and, ultimately, the perception of light. The goal of this thesis is to investigate natural variation in rhodopsin function in the context of evolutionary adaptation, chromophore usage, and disease mutations. Following a general introduction, in Chapter II, I characterize the visual system of the diurnal colubrid snake Pituophis melanoleucus using immunohistochemistry of retinal sections and spectroscopy of purified visual pigments expressed in vitro, revealing an unusual rhodopsin with cone opsin properties found in cone-like rod photoreceptors. In Chapter III, I investigate the effects of the rare vertebrate chromophore, 11-cis 3,4 dehydroretinal (A2), on the spectral and non-spectral properties of rhodopsin. In Chapters IV and V, I study the effects of pathogenic mutations in rhodopsin that cause the retinal degenerative disease retinitis pigmentosa (RP). In Chapter IV of my thesis, I identify the phenotype of RP mutations found in the extracellular loop 2 of rhodopsin and assess the effects of functional rescue using two different approaches. Finally, in Chapter V, I characterize three novel RP mutations to investigate the relationship between the in vitro and clinical disease phenotypes. The investigations in this thesis expand our understanding of snake retinal evolution, the role of the chromophore in rhodopsin function, and the effect of pathogenic mutations on rhodopsin structure and function. This thesis combines data from non-model organisms, non-mammalian chromophores, and non-wildtype pathogenic mutations to significantly increase our understanding of the scope of rhodopsin functionality.