Structure of the manganese complex of photosystem II upon removal of the 33-kilodalton extrinsic protein: an X-ray absorption spectroscopy study.

The structure of the Mn complex of photosystem II (PSII) was studied by X-ray absorption spectroscopy. Oxygen-evolving spinach PSII membranes containing 4-5 Mn/PSII were treated with 0.8 M CaCl2 to extract the 33-, 24-, and 16-kilodalton (kDa) extrinsic membrane proteins. Mn was not released by this treatment, but subsequent incubation at low Cl- concentration generated preparations containing 2 Mn/PSII. The Mn X-ray absorption K-edge spectrum of the CaCl2-washed preparation containing 4 Mn/PSII is very similar to spectrum of native PSII, indicating that the oxidation states and ligand symmetry of the Mn complex in these preparations are not significantly different. The Mn extended X-ray absorption fine structure (EXAFS) of CaCl2-washed PSII fits to a Mn neighbor at approximately 2.75 A and two shells of N or O at approximately 1.78 and approximately 1.92 A. These distances are similar to those we have previously reported for native PSII preparations [Yachandra, V. K., Guiles, R. D., McDermott, A. E., Cole, J. L., Britt, R. D., Dexheimer, S. L., Sauer, K., & Klein, M. P. (1987) Biochemistry (following paper in this issue)] and are indicative of an oxo-bridged Mn complex. Our results demonstrate that the structure of the Mn complex is largely unaffected by removal of 33-, 24-, and 16-kDa extrinsic proteins, do not provide ligands to Mn. The Mn K-edge spectrum of the CaCl2-washed sample containing 2 Mn/PSII has a dramatically altered shape, and the edge inflection point is shifted to lower energy. The position of the edge is consistent with a Mn oxidation state of +3.(ABSTRACT TRUNCATED AT 250 WORDS)