Demonstration of single molecule spectroscopy on large autofluorescent protein complexes
Single molecule spectroscopy enables the detection of the structural and functional dynamics of the molecular machinery of the cell at the ultimate level of sensitivity. Using fluorescence as a sensitive reporter, interactions between individual biomolecules can be quantified, macromolecules can be tracked, and their behaviour can be revealed, information that is often hidden in standard ensemble approaches. In this presentation, the usefulness of single molecule spectroscopy will be demonstrated on a few autofluorescent pigment-binding protein complexes. It will be shown how this method has revealed previously unknown functional states in light-harvesting complexes from plants, diatoms, and cyanobacteria, states that are hidden in the ensemble average. We have thoroughly characterised these new states, fully or partly resolved the underlying molecular mechanisms, and related them to specific conformational states of the proteins. We have been able to control in real time the interaction between two physiological partners in cyanobacteria and thus revealed a docking mechanism. Finally, it will be demonstrated how the function of these protein complexes can be drastically modified by interfacing them with metallic nanostructures and ensuring a significant overlap between the optical transitions of the complexes and the nanostructures to dramatically alter the radiative and nonradiative deexcitation rates.
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University of Pretoria