Correlation between Protein Flexibility and Electron Transfer from to Q_Bin PSII Membrane Fragments from Spinach

Abstract

To analyze a possible correlation between the extent of QA-* reoxidation and protein dynamics, fluorometric and Mössbauer spectroscopic measurements were performed in photosystem II membrane fragments from spinach. Numerical evaluation of the flash-induced change of the normalized fluorescence quantum yield revealed that the extent of reoxidation starts to decrease below 275 K and is almost completely suppressed at 230 K. Detailed analyses of Mössbauer spectra measured at different temperatures in 57Fe-enriched material indicate that the onset of fluctuations between conformational substates of the protein matrix occurs also at around 230 K. Based on this correspondence, protein flexibility is inferred to play a key role for QA-* reoxidation in photosystem II. Taking into account the striking similarities with purple bacteria and the latest structural information on these reaction centers [Stowell, M. H. B., McPhillips, T. M., Rees, D. C., Soltis, S. M., Abresch, E., and Feher, G. (1997) Science 276, 812-816], it appears most plausible that also the headgroup of plastoquinone-9 bound to the QB-site in PSII requires a structural reorientation for its reduction to the semiquinone.

The functional role of protein dynamics in photosynthetic reaction centers investigated by elastic and quasielastic neutron scattering

“…[1,2,10,23]). It is interesting to note that a similar correlation between molecular dynamics and Q A → Q B electron transfer was observed in the bacterial RC [24]. Indeed, in the case of the RC of Rhodobacter sphaeroides a reorientation of the Q B headgroup upon electron uptake was reported based on X-ray crystallography as shown in Fig.…”

Influence of Cd2+on the spin state of non-heme iron and on protein local motions in reactions centers from purple photosynthetic bacteriumRhodospirilium rubrum

“…Finally, the spectrum obtained for the control sample of chromatophores contains a third component with IS = 0.97 ± 0.02 mm/s and QS = 2.53 ± 0.14 mm/s, typical hyperfine parameters for the high spin Fe 2+ state. This component is usually ascribed to NHFe, which high spin ferrous state in photosynthetic RC of type Q is well known [10,18]. In order to improve the fit of the spectrum collected for control RCs one can also add a minor contribution of this high spin ferrous state but IS in this case is shifted to 1.18 ± 0.10 mm/s.…”

“…In particular, the role of NHFe, a very conservative component of the Q-type RCs, in photosynthetic charge separation and the temperature effects on ET between the two external quinone acceptors are among the most challenging issues [7,8]. Intriguingly, ET from reduced Q A to Q B is inhibited at temperatures below 200±20 K whereas Q A in RCs from various organisms remains fully active at cryogenic temperatures [9,10]. This is in line with the theoretical calculations which suggest that some intrinsic flexibility of the protein matrix in the vicinity of the Q A -Fe-Q B complex is required for efficient ET on the RCs acceptor side [11].…”

Herbicide resistance and supersensitivity in photosystem II

“…The electron is transported via pheophytin to Q A and ultimately to Q B . The head group of plastoquinone bound to the Q B -site in photosystem II requires a structural reorientation for its reduction to the semiquinone [36]. The double-reduced Q B 2 − gets protonated and leaves the binding pocket.…”