title: Dynamic properties of photosystem II membranes at physiological temperatures characterized by elastic incoherent neutron scattering. Increased flexibility associated with the inactivation of the oxygen evolving complex.
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.
authors: Institut Laue-Langevin, P.O. Box 156, 38042, Grenoble Cedex 9, France.
authors: Gergely
authors: G
authors: Nagy
authors: Jörg
authors: J
authors: Pieper
authors: Sashka B
authors: SB
authors: Krumova
authors: László
authors: L
authors: Kovács
authors: Marcus
authors: M
authors: Trapp
authors: Győző
authors: G
authors: Garab
authors: Judith
authors: J
authors: Peters
mesh_terms: D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D033363:Neutron Diffraction; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D012542:Scattering, Radiation; D018724:Spinacia oleracea / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D020524:Thylakoids / Q000737:chemistry / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D010100:Oxygen