title: Temperature- and hydration-dependent protein dynamics in photosystem II of green plants studied by quasielastic neutron scattering.
abstract: Protein dynamics in hydrated and vacuum-dried photosystem II (PS II) membrane fragments from spinach has been investigated by quasielastic neutron scattering (QENS) in the temperature range between 5 and 300 K. Three distinct temperature ranges can be clearly distinguished by active type(s) of protein dynamics: (A) At low temperatures (T < 120 K), the protein dynamics of both dry and hydrated PS II is characterized by harmonic vibrational motions. (B) In the intermediate temperature range (120 < T < 240 K), the total mean square displacement <u2>total slightly deviates from the predicted linear behavior. The QENS data indicate that this deviation, which is virtually independent of the extent of hydration, is due to a partial onset of diffusive protein motions. (C) At temperatures above 240 K, the protein flexibility drastically changes because of the onset of diffusive (large-amplitude) protein motions. This dynamical transition is clearly hydration-dependent since it is strongly suppressed in dry PS II. The thermally activated onset of protein flexibility as monitored by QENS is found to be strictly correlated with the temperature-dependent increase of the electron transport efficiency from Q(A)(-) to QB (Garbers et al. (1998) Biochemistry 37, 11399-11404). Analogously, the freezing of protein mobility by dehydration in dry PS II appears to be responsible for the blockage of Q(A)(-) reoxidation by Q(B) at hydration values lower than 45% r.h. (Kaminskaya et al. (2003) Biochemistry 42, 8119-8132). Similar effects were observed for reactions of the water-oxidizing complex as outlined in the Discussion section.
authors.affiliation: Max-Volmer-Laboratories for Biophysical Chemistry, Technische Universität Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany. joerg.pieper@tu-berlin.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Pieper
authors.forename: Thomas
authors.initials: T
authors.lastname: Hauss
authors.forename: Alexandra
authors.initials: A
authors.lastname: Buchsteiner
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Baczyński
authors.forename: Karolina
authors.initials: K
authors.lastname: Adamiak
authors.forename: Ruep E
authors.initials: RE
authors.lastname: Lechner
authors.forename: Gernot
authors.initials: G
authors.lastname: Renger
mesh_terms: D007700:Kinetics; D009502:Neutrons; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D018724:Spinacia oleracea / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D014867:Water