Spatial dynamics of electron transport

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The thylakoid membranes of cyanobacteria contain both photosynthetic and respiratory electron transport complexes. This allows the possibility of multiple electron transport routes, including routes in which electrons are transferred from respiratory donors to photosynthetic acceptors, and vice versa. The routes taken by electrons are crucial for cellular physiology, since they control both the redox balance of the cell and its main means of energy conversion. The question we wish to address in this proposal is what controls the probability of the different possible electron pathways. The problem in cyanobacteria is a specific example of a more general problem in bioenergetic membranes. Our current results strongly suggest that routes of electron transport in the cyanobacterium Synechococcus 7942 (and in other organisms) are controlled by lateral heterogeneity in the membrane on the sub-micron scale. This heterogeneity is on a large enough scale to be visualisable by GFP-tagging and fluorescence microscopy. In this project we will further define the composition and structure of zones in the Synechococcus membrane in which respiratory complexes are concentrated, initially by further fluorescent tagging and confocal microscopy, then using biochemical approaches and electron microscopy. We will use spectroscopic techniques to determine the effects that membrane heterogeneity has on electron transport pathways. We will investigate the signal transduction mechanisms that regulate the lateral distribution of complexes, in terms of the initial triggering signals and in terms of the downstream factors that lead to re-organisation of the membrane. We will combine this with an investigation of the dynamic behaviour of quinone electron carriers in bioenergetic membranes, in order to get a complete picture of the way in which electron transport pathways in an intact bioenergetic membrane relate to the mobility and distribution of the electron carriers.

Please refer to Lead Application