Abstract
Elastic incoherent neutron scattering (EINS), a non-invasive technique which is capable of measuring the mean square displacement of atoms in the sample, has been widely used in biology for exploring the dynamics of proteins and lipid membranes but studies on photosynthetic systems are scarce. In this study we investigated the dynamic characteristics of Photosystem II (PSII) membrane fragments between 280 and 340 K, i.e., in the physiological temperature range and in the range of thermal denaturation of some of the protein complexes. The mean square displacement values revealed the presence of a hydration-sensitive transition in the sample between 310 and 320 K, suggesting that the oxygen evolving complex (OEC) plays an important role in the transition. Indeed, in samples in which the OEC had been removed by TRIS- or heat-treatments (323 and 333 K) no such transition was found. Further support on the main role of OEC in these reorganizations is provided by data obtained from differential scanning calorimetry experiments, showing marked differences between the untreated and TRIS-treated samples. In contrast, circular dichroism spectra exhibited only minor changes in the excitonic interactions below 323 K, showing that the molecular organization of the pigment-protein complexes remains essentially unaffected. Our data, along with earlier incoherent neutron scattering data on PSII membranes at cryogenic temperatures (Pieper et al., Biochemistry 46:11398-11409, 2007), demonstrate that this technique can be applied to characterize the dynamic features of PSII membranes, and can be used to investigate photosynthetic membranes under physiologically relevant experimental conditions.
| Original language | English |
|---|---|
| Pages (from-to) | 113-124 |
| Number of pages | 12 |
| Journal | Photosynthesis Research |
| Volume | 111 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Mar 2012 |
| Externally published | Yes |
Funding
Acknowledgments We would like to thank the Institut Laue-Langevin (Grenoble, France) for providing us beamtime for the experiments. We are indebted for Dr. Francesca Natali and Teddy Carriere (ILL., Grenoble) for helping us with the configuration of the experiments. We also wish to thank Dr. Zsuzsanna Várkonyi and Dr. Ottó Zsíros (BRC, Szeged) for participating in the preparation of BBY samples, Dr. Mira Busheva and Svetla Todinova for the DSC measurements and Dr. Stuart Fisher for the calculations of the isotopic composition of the protein complexes in the investigated sample. This study was supported by the Marie Curie Initial Training Network ‘HARVEST’ sponsored by the 7th Framework Program of the European Union [No. 238017] and by the Hungarian Scientific Research Fund/National Office for Research and Technology [No. 80345] grants to G. G. and Bourse du Gouvernement Franc¸ais to G.N.; J. P. gratefully acknowledges support by the European Social Fund’s Doctoral Studies and Internationalisation Programme DoRa.
Keywords
- Elastic incoherent neutron scattering
- Oxygen evolving complex Photosystem II
- Protein dynamics
- Thermal stability