Expression of the 23 kDa protein from the oxygen-evolving complex of higher plants in Escherichia coli.

The 23 kDa protein from the oxygen-evolving complex of higher plants regulates the binding of one Ca2+ ion, which is an essential cofactor of water splitting. In this report its expression in Escherichia coli is described. The 23 kDa protein was expressed and secreted to the periplasm where it accumulated in a soluble form. After purification by cation exchange chromatography the recombinant protein was found to NaCl-washed Photosystem II. Detailed analysis of oxygen-evolving activity demonstrates its function in Ca2+ binding identical to the spinach 23 kDa protein. This expression system opens the way for mutational analysis and isotopic labelling in order to study its function in water splitting.