A comparative look at structure-function roles in light-harvesting dynamics of purple bacteria

Abstract

Using a unique approach to solar energy conversion, photosynthetic organisms have developed a light-harvesting process with near unity quantum efficiency. Light-harvesting proteins transfer energy from the sun to reach a central location, the reaction center, where charge separation occurs and energy is converted to chemical energy. Moreover, these proteins are able to carry out this efficient transfer in cellular membranes despite the complex environment found in these membranes. Particularly, light-harvesting in photosynthetic purple bacteria uses a diverse set of tools from species to species to efficiently transfer energy through this protein network. Induced by their habitats, external environmental pressures on the fitness of purple bacteria have caused species to evolve different mechanisms in order to deal with thesel pressures. Although these complexes have been studied for some time, there is still very little known about particular species.

Additionally, most previous work has been on non-native samples, such as detergent solubilized proteins, or on complex membranes such as vesicles, chromatophores, or whole membranes that contain multiple proteins with multiple processes occurring simultaneously. This work investigates how photosynthetic light-harvesting complexes are able to achieve their impressive efficiency using ensemble ultrafast spectroscopy to measure energy transfer dynamics and near-native discoidal model membrane-discs. These model membrane-discs provide a controlled environment to effectively study how energy is transferred in a single protein and between particular sets of proteins, allowing individual steps in the light-harvesting process to be probed without other processes interfering. They also provide a near-native system to explore how lipid-protein and protein-protein interactions affect the energy transfer kinetics in these proteins.

Additionally, this work explores the differences in energy transfer kinetics of light-harvesting proteins between species of purple bacteria. Overall, this provides new insights into the role the membrane plays in light-harvesting and how the composition of proteins within the native membrane of different species of purple bacteria can add variation to energy transfer kinetics.