COORDINATION SPHERE AND STRUCTURE OF THE MN CLUSTER OF THE OXYGEN-EVOLVING COMPLEX IN PHOTOSYNTHETIC ORGANISMS

The great similarity between the binding of Fe(II) and the high-affini ty Mn-binding site in the Mn-depleted PSII membranes (Semin et al. (19 96) PEES Lett. 375, 223-226) suggests that the coordination sphere of Mn in PSII is also suitable for iron. A comparison is performed betwee n the primary amino acid sequences of D1 and D2 and diiron-oxo enzymes with the function of oxygen activation. All conservative motifs (EXXH ) and residues binding and stabilizing the diiron cluster in diiron-ox o enzymes have been found in the C-terminal domains of DI and D2 polyp eptides. On the basis of these sequence similarities we suggest a stru ctural model for the manganese cluster in the oxygen-evolving complex.