Biological activity of retinal proteins is related to a photocycle during which both the retinal and the opsin moieties undergo a series of structural changes. The molecular changes and their correlation with the corresponding biological functions are of primary importance. Clarifying these functions may be achieved by obtaining a structural description of the polyene chromophore, its spectroscopic properties at the binding site, its opsin environment, and the changes occurring in retinal-opsin interactions following light absorption. Using artificial pigments, model compounds in solution and spectroscopic methods (absorption, FTIR, NMR and AFM), we have shed light on the role that single and double bonds play in the photocycle, protein-chromophore interactions in the binding site and the role of water and light in retinal protein activity.
Bacteriorhodopsin (bR) is a retinal protein which serves as a light-driven proton-pumping membrane protein, arranged in a 2D hexagonal lattice, usually found in crystalline purple membrane patches (PM). We have checked the possibility that bacteriorhodopsin can transport efficiently not only protons but also electrons. Therefore, electronic transport (ETp) in wild-type and different variants of bR has been studied. Strikingly, we have revealed that bR transports remarkably high current densities above room temperature. Further work is carried out to unravel the mechanism of electronic transport via retinal proteins.