CONESYSTEM · Vision in color: Molecular mechanism of the color visual system

Vision in color: Molecular mechanism of the color visual system

The retina of vertebrates contains two kinds of photoreceptor cells, the abundant rod cells, containing the rhodopsin pigment, and the much scarcer cone cells, with the blue, green and red cone pigments. These pigments belong to the superfamily of G-protein coupled receptors and upon photoactivation interact and activate a specific heterotrimeric G protein, transducin, initiating the visual signalling phototransduction cascade. Mutations in the cone pigments have been reported to cause cone cells dystrophies. The main goal of this project was to provide an overall picture that integrates in a coherent scheme the molecular basis of cone degeneration due to mutations found in cone pigments. To do that, these proteins were expressed, and characterized by means of spectroscopic techniques. Here we also expressed and purified cone transducin, and GTPγS35 binding assay has been carried out in order to determine its activity. Surface Plasmon Resonance (SPR) spectroscopy, technique used to study the protein-protein binding kinetics, was also performed to determine the kinetic features of the biomolecular interactions between the visual pigments and transducin. Initially, we used rhodopsin in order to find the right conditions before using the inherently unstable cone pigments. Our results show that most of these mutants cannot be purified by using the traditional immunopurification protocol. Cone transducin was expressed and used for a G-protein activation assay. SPR spectroscopy was also used to determine the kinetics of binding and we found that the system still needs some work in order to successfully bind the cone transducin with its receptor. Characterization of cone pigments mutants that may cause color blindness and other visual dystrophies is an advance on the state-of-the-art within the visual diseases arena. The cone opsins are normally studied by their characteristic spectral tuning, which makes each pigment specific for a wavelength range. These pigments are not well characterized and advances on the molecular pathways causing visual disorders are not well understood. Here we have characterized the structure-function relationship in the least known human photopigment, the cone pigment. Dr Ramon is currently in process of getting accreditation to apply to a tenure-track lecturer position, which is the first contractual position in the Spanish system. The nature of this contract is temporary and full-time. The contract can last up to five years, and with full teaching and research autonomy. Overall, our results provide more light into the cone pigment system which has not been widely studied due to the scarcer amount in nature. Since most of the information available on cone pigment phototransduction is extrapolated from the rod system, our contribution represents an advance in our knowledge of this system and in the visual system arena. As for the prospects to be permanently reintegrated to the host institution; unfortunately that would depend upon on budget’s institution rather than Dr. Ramon scientific and laboratory management expertise acquired during the development of this project.

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