Electronic and spatial characteristics of the retinylidene chromophore of rhodopsin

The G protein coupled receptor rhodopsin was characterised by physical chemical methods like solid-state NMR, FTIR and UV/Vis spectroscopy. Goal of the research was to determine the impact of steric and electronic properties of the retinal ligand on the rate and efficiency of the photochemical reaction of this light activated receptor. First the required 13C labelled and chemically modified retinal derivatives were obtained by chemical synthesis. Subsequently, solid-state 13C NMR was used as a tool to characterise the electronic structure of the native ligand bound to rhodopsin, while FTIR difference spectroscopy was applied to determine the effect retinal ligands that were modified in the isomerisation region. It transpires that the combined approach of synthesis and spectroscopic techniques can reveal fundamental aspects of the interplay of the electronic properties and the spatial arrangement of the ligand that may ultimately allow a more profound understanding of the activation of GPCRs, in addition to knowledge about the ultrafast and efficient isomerisation of the retinylidene chromophore in rhodopsin