Functional characteristics and associated structural features of mammalian melanopsin photopigments (360G-Wellcome-078808_A_05_Z)

Melanopsin (a member of the opsin family of G protein coupled receptors) is thought to be the photopigment of recently discovered inner retinal photoreceptors in mammals. To allow direct functional analysis of this protein we have lately developed methods for its heterologous expression in cell culture and shown that, under these conditions, it binds retinal to form a photosensory complex with the ability to regulate cell activity via G-protein signalling. Here we propose building on our heterologous expression breakthrough to conclude a detailed functional and structural analysis of this protein based around 3 goals.Goal 1. To consolidate our functional analysis of human and mouse melanopsins using spectroscopic, physiological and biochemical approaches to elucidate aspects of its photochemistry (especially its spectral sensitivity and photoactivation) and G protein coupling.Goal 2. To generate an accurate 3D structure of melanopsin, based initially upon an empirical computer model, and refined according to experimental examination (cf goal 3) and 2D/3D crystallography.Goal 3. To establish critical structure:function relationships for melanopsin by using our developing structural understanding to define suitable site directed mutants and exposing them to detailed functional analysis.