Final Report Summary - DODECIN (Construction of a Molecular Crane Based on the Flavoprotein Dodecin) Dodecin from Halobacterium salinarum is a dodecameric multi-ligand binding flavoprotein. While dodecin binds flavin ligands with high affinity when they are oxidized, flavin reduction induces dissociation of the holoprotein into apoprotein and free flavins. In the current project the redox-active protein dodecin has been reconstituted on flavin-terminated DNA monolayers. Multiple and reversible dodecin reconstitution and disintegration by chemical flavin reduction could be carried out several times at the same surface. Stable protein-DNA monolayers could be obtained via multi-ligand binding at high flavin surface density, i.e. if one apododecin binds to two or more surface tethered flavins. While the holoprotein complex could be easily and quantitatively disassembled by chemical flavin reduction, electrochemical flavin reduction via direct electron transfer through the double-stranded DNA tethers was not possible. Further systems such as carbon nanotubes, redox-active rotaxane architectures, and organic pi-electron systems, which were evaluated as an alternative to DNA, were not suitable for an application as molecular wire, since at these systems strong non-specific protein adsorption was observed. Nevertheless we were able to switch the binding and release of apododecin at flavin-terminated DNA monolayers electrochemically by a change in the applied redox potential in the presence of selected redox mediators. Based on these results it is possible to further miniaturize the system down to the single molecule level allowing the binding and release (and thus the transport) of single apoprotein molecules. On top of protein-DNA layers on surfaces additional bi-or multidentate flavin-DNA ligands can be bound in a sandwich-type assembly. Dodecin has been introduced as a key element for the multiple (re)programming of protein-DNA nanostructures comprising generation, deletion and re-programming on the same flavin-DNA modified surface. Hence the versatile concept of reprogrammable functional biointerfaces with the multi-ligand binding flavoprotein dodecin has been demonstrated.Based on the progress in the design and investigation of protein-DNA surface architectures a new strategy for the generation of pristine DNA hydrogels could be developed. These hydrogels are of strong interest for biomedical applications. Furthermore different types of optical biosensors for the detection of specific oligonucleotide sequences with surface plasmon fluorescence spectroscopy as the readout technique have been implemented. In addition a spectroelectrochemical setup for the determination of protein redox potentials developed and applied for the determination of the redox potential of glucose oxidase at different pH values.
