Abstract
The structure of the cytochrome b6f complex from the thermophilic cyanobacterium, M. laminosus, has been solved to a resolution of 3.0 angstrome, thus completing the structural description of the architecture of the electron transport chain of oxygenic photosynthesis. The crystal structure shows that two monomers of an eight subunit dimeric complex surround a large inter-monomer cavity stabilized by lipids. The cavity reveals the quinone exchange pathway through a plastoquinone near a unique heme on the electronegative side of the cavity, and a quinone analogue inhibitor on the electropositive side that occludes a portal to the [2Fe-2S] cluster and bp-heme. It is proposed that the mechanism of electron transfer from plastoquinol to the cytochrome f heme involves a small amplitude tethered rotation of the [2Fe-2S] protein about its hinge and the possible electron transfer around the unique heme for Fd-dependent cyclic electron transport.
