Construction and analysis of minimized water-splitting reaction system from cyanobacterial photosystem II

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Water-splitting reaction in photosystem II (PSII) relies on redox cofactors all of which bind on D1/D2 hererodimeric subunits (psbA and psbD gene products). We hypothesized that D1/D2 heterodimer could intrinsically carry out the PS II redox reaction in its isolated state. To prove this, we set the following experimental scheme: (1) construction of Synechococcus elongatus PCC 7942 strains expressing only psbA and psbD genes from a thermophilic cyanobacterium, (2) purification of PS II complex from the recombinant strains using CP47-histag affinity chromatography, (3) heat destruction of the PS II complex followed by chromatographic purification of thermostable D1/D2 heterodimer, and (4) reconstitution of Mn4Ca cluster on D1/D2 heterodimer. Here, we describe our recent progress in step (1) and (2).