Light-induced water oxidation in photosystem II
Frank Muh1,2, Athina Zouni2
1
Institut fur Chemie und Biochemie/Kristallographie, Freie Universitat Berlin, Fabeckstrasse 36a, D-14195 Berlin, Germany, 2Max-Volmer-Laboratorium fur Biophysikalische Chemie, Technische Universitat Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
TABLE OF CONTENTS
- 1. Abstract
- 2. Introduction
- 3. Excitation enery transfer, charge separation, and quinone reduction
- 3.1. Excitation energy transfer and charge separation
- 3.2. Non-heme iron and quinones
- 3.3. Creation of a strong oxidant
- 4. Redox states of the Mn4Ca-cluster
- 4.1. Kok-cycle and S-states
- 4.2. X-ray spectroscopy
- 4.3. Electron paramagnetic resonance (EPR) spectroscopy
- 4.4. Electron nuclear double resonance (ENDOR) spectroscopy
- 4.5. Chemical reduction of the Mn4Ca-cluster
- 4.6. Net charge changes of the Mn4Ca-cluster
- 5. Structure of the Mn4Ca-cluster
- 5.1. X-ray crystallography
- 5.2. Extended X-ray absorption fine structure (EXAFS)
- 5.3. Ca site and Ca/Sr exchange
- 5.4. EPR/ENDOR spectroscopy
- 5.5. Ligand sphere of the Mn4Ca-cluster
- 5.5.1. Asp A170
- 5.5.2. Glu A189
- 5.5.3. His A332
- 5.5.4. Glu A333
- 5.5.5. His A337
- 5.5.6. Asp A342
- 5.5.7. C-terminal Ala A344
- 5.5.8. Glu C354
- 6. Educt and product channels
- 6.1. Channel proposals
- 6.2. Channel calculations
- 6.3. Noble gas pressurization
- 7. Chloride binding sites
- 8. Redox-active tyrosines
- 8.1. YZ
- 8.2. Metalloradical signals of YZ
- 8.3. YD
- 9. Proton release
- 10. Water binding, water consumption, and oxygen release
- 10.1. Water binding sites
- 10.2. Water insertion and consumption
- 10.3. Dioxygen formation and release
- 11. Conclusion and Perspectives
- 12. Acknowledgments
- 13. References
1. ABSTRACT
The photosystem II core complex (PSIIcc) is the key enzyme of oxygenic photosynthesis, as it catalyzes the light-induced oxidation of water to form dioxgyen and protons. It is located in the thylakoid membrane of cyanobacteria, algae, and plants and consists of 20 protein subunits binding about 100 cofactors. In this review, we discuss what is presently known about the "donor side" of PSIIcc, covering the photosynthetic reaction center and the water oxidase part. The focus is on the catalytic Mn4Ca cluster and its protein environment. An attempt is made to connect recent crystallographic data (up to 2.9 Å resolution) with the wealth of information about Nature´s water oxidation device from spectroscopic, biochemical and theoretical work.
