PS II unveiled

The photosynthetic enzyme Photosystem II (PSII) generates all of Earth?s atmospheric oxygen through a thermodynamically unfavorable reaction, splitting water into hydrogen and oxygen using solar energy. ?It?s been the Holy Grail of photosynthesis research ? to obtain structural information about the catalytic center where this very remarkable reaction occurs,? says biochemist James Barber of Imperial College London.

Barber and colleagues? 3.5 angstrom structure of a cyanobacterial PSII represented the highest resolution to date obtained for the enzyme, and revealed the oxygen-evolving center (OEC) as a cubane-like structure consisting of three manganese ions and one calcium ion, surrounded by amino acids that either act as ligands to the metal ions or make up the cavity in which the water-splitting reaction occurs.1 A fourth manganese ion linked to the cube facilitates the reaction, Barber says.

Beyond overcoming the significant challenges of crystallizing a membrane-bound protein,...