Controlling Photosynthetic Light Harvesting at the Single Protein Level

Abstract

The light-harvesting complexes of oxygenic photosynthetic organisms have to balance two vital functions: efficient transport of photoexcitations to the photochemical reaction center under low levels of solar radiation and efficient photoprotection under intense solar radiation and other stress conditions, during which photoexcitations are rapidly dissipated as heat. Most light-harvesting proteins bind a dense arrangement of chromophores, ensuring that subtle protein conformational changes are often sufficient to switch between the complexes’ light-harvesting and photoprotective functions. Single-molecule spectroscopy allows one to follow these switches in real time. I will show how this technique has led to the discovery of new light-harvesting and photoprotective states in various photosynthetic light-harvesting complexes and how the population equilibrium between these states can be finely tuned at the single protein level by the incident photon flux, the pH, the chromophore arrangement, and by controlling the interaction with small, accessory proteins. I will also demonstrate how the light-harvesting efficiency of these complexes can be actively controlled through interactions with localized surface plasmons from metallic nanostructures to dramatically alter the radiative and nonradiative deexcitation rates.