Functional domains in melanopsin: natural variants and molecular engineering

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Rods and cones are light sensitive cells in the retina responsible for dim light vision and colour vision. More recently a third type of light sensitive cell has been found in the retina, which express the blue-light sensitive protein called melanopsin. These cells, termed photosensitive retinal ganglion cells (pRGCs), send connections to numerous structures within the brain and control a range of non visual responses to light including the induction of sleep, pupil light reflexes and entrainment to daily light cycles. More recently these cells have been shown to perform roles in visual pathways, mood and depression, and are emerging as a key biological pathway regulating human physiology and health.Mutations in the light sensitive molecules of rods and cones lead to a range of retinal diseases and are a leading cause of blindness. Mutation and polymorphisms in melanopsin have also been detected in the human population, resulting in changes in physiological responses to light and have been associated with seasonal affective disorder. Understanding the consequences of mutations on the properties of melanopsin is fundamental to predicting their effects on human physiology and health. As with all biological molecules, the structure of melanopsin is key to its function. However the functional roles performed by the different regions of the melanopsin molecule are not well established. In this study we will produce a number of melanopsin molecules containing targeted changes within specific regions of the protein, as a means to determining the roles performed by these regions in a number of key functions. Principally we will focus on modelling the mutations known to be present in the human population, and determine the general roles performed by areas of the molecule in which these mutations are found. In addition, we will determine the regions of the melanopsin protein that influence sensitivity to light and specifically the colour of light to which this protein responds (termed spectral tuning sites). Similar studies have been conducted for the light sensitive 'opsin' molecules found in rods and cones, yet melanopsin represents a functionally different class of opsin with important functional and structural differences. To date no study has investigated the spectral tuning of this class of 'non-visual' opsin. As a consequence of this study we will generate a range of melanopsin variants that respond to different colours of light. Such variants have huge potential for research applications, where the expression of melanopsin can be used to confer sensitivity to light and allow the selective activation of cell types of interest both in vitro and in vivo, and also for gene therapy based approaches aimed at treating retinal disease and restoring vision. This programme of work will lead to a fundamental increase in our understanding of the melanopsin protein, a protein that performs important roles in human physiology and health. This study will also provide a range of new research tools that are applicable to a wide range of biological research fields and also the development of novel tools for the treatment of human disease.