High-resolution Mn EXAFS of the oxygen-evolving complex in photosystem II: structural implications for the Mn4Ca cluster.
The biological generation of oxygen by the oxygen-evolving complex in photosystem II (PS II) is one of nature's most important reactions. The recent X-ray crystal structures, while limited by resolutions of 3.2-3.5 A, have located the electron density associated with the Mn4Ca cluster within the multiprotein PS II complex. Detailed structures critically depend on input from spectroscopic techniques, such as EXAFS and EPR/ENDOR, as the XRD resolution does not allow for accurate determination of the position of Mn/Ca or the bridging and terminal ligand atoms. The number and distances of Mn-Mn/Ca/ligand interactions determined from EXAFS provide important constraints for the structure of the Mn4Ca cluster. Here, we present data from a high-resolution EXAFS method using a novel multicrystal monochromator that show three short Mn-Mn distances between 2.7 and 2.8 A and, hence, the presence of three di-mu-oxo-bridged units in the Mn4Ca cluster. This result imposes clear limitations on the proposed structures based on spectroscopic and diffraction data and provides input for refining such structures.
Yano
Junko
J
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Pushkar
Yulia
Y
Glatzel
Pieter
P
Lewis
Azul
A
Sauer
Kenneth
K
Messinger
Johannes
J
Bergmann
Uwe
U
Yachandra
Vittal
V
D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism
D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen; D002118:Calcium