Structure and Orientation of the Mn4Ca Cluster in PlantPhotosystem II Membranes Studied by Polarized Range-Extended X-rayAbsorption Spectroscopy
X-ray absorption spectroscopy has provided importantinsights into the structure and function of the Mn4Ca cluster in theoxygen-evolving complex (OEC) of Photosystem II (PS II). The range of Mnextended X-ray absorption fine structure (EXAFS) data collected from PSII until now has been, however, limited by the presence of Fe in PS II.Using a crystal spectrometer with high energy resolution to detect solelythe Mn K alpha fluorescence, we are able to extend the EXAFS range beyondthe onset of the Fe absorption edge. This results in improvement inresolution of the Mn-backscatterer distances in PS II from 0.14 Angstromto 0.09 Angstrom. The high-resolution data obtained from oriented spinachPS II membranes in the S1 state show that there are threedi-?-oxo-bridged Mn-Mn distances of ~;2.7 Angstrom and ~;2.8 Angstrom ina 2:1 ratio and that these three Mn-Mn vectors are aligned at an averageorientation of ~;60 deg relative to the membrane normal. Furthermore, weare able to observe the separation of the Fourier peaks corresponding tothe ~;3.2 Angstrom Mn-Mn and the ~;3.4 Angstrom Mn-Ca interactions inoriented PS II samples and determine their orientation relative to themembrane normal. The average of the Mn-Ca vectors at ~;3.4 Angstrom isaligned along the membrane normal, while the ~;3.2 Angstrom Mn-Mn vectoris oriented near the membrane plane. A comparison of this structuralinformation with the proposed Mn4Ca cluster models based on spectroscopicand diffraction data provide input for refining and selecting among thesemodels.
- Research Organization:
- Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE Director, Office of Science; National Institutes ofHealth
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 920335
- Report Number(s):
- LBNL--60491; BnR: KC0304000
- Journal Information:
- The Journal of Biological Chemistry, Journal Name: The Journal of Biological Chemistry Journal Issue: 10 Vol. 282
- Country of Publication:
- United States
- Language:
- English
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