Spare quinones in the QB cavity of crystallized photosystem II from Thermosynechococcus elongatus

Abstract

The recent crystallographic structure at 3.0 A resolution of PSII from Thermosynechococcus elongatus has revealed a cavity in the protein which connects the membrane phase to the binding pocket of the secondary plastoquinone Q(B). The cavity may serve as a quinone diffusion pathway. By fluorescence methods, electron transfer at the donor and acceptor sides was investigated in the same membrane-free PSII core particle preparation from T. elongatus prior to and after crystallization; PSII membrane fragments from spinach were studied as a reference. The data suggest selective enrichment of those PSII centers in the crystal that are intact with respect to O(2) evolution at the manganese-calcium complex of water oxidation and with respect to the integrity of the quinone binding site. One and more functional quinone molecules (per PSII monomer) besides of Q(A) and Q(B) were found in the crystallized PSII. We propose that the extra quinones are located in the Q(B) cavity and serve as a PSII intrinsic pool of electron acceptors.

Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis

“…The XAS samples contained the intrinsic electron acceptors of PSII, namely Q A , Q B , and two or three additional plastoquinones per PSII reaction center, as verified by prompt chlorophyll fluorescence measurements (supplemental information, section 3), which revealed that on the average at least eight electrons could be transferred to the PSII acceptor side, in agreement with previous results (8,37) X-ray Absorption Experiments on Non-heme Iron-The Fe K-edge spectrum of dark-adapted preoxidized PSII samples ( Fig. 2A) showed an edge energy of 7124.3 eV (at 50% level), indicating the prevalence of Fe(III), as expected (supplemental information, section 2).…”

Time-resolved X-ray spectroscopy leads to an extension of the classical S-state cycle model of photosynthetic oxygen evolution

“…Rather than being a first-sphere ligand of manganese, the halide may be at a distance of~5 Å to Mn or Ca-at least in the S 1 -state complex . Further details of the PSII structure have been revealed in 2005 by Zouni, Saenger and their coworkers , inter alia a putative channel possibly filled with 1-2 structurally disordered plastoquinones (Krivanek et al 2007).…”

Comparative analysis of plant lycopene cyclases

“…It should also be mentioned that photosystem II, multisubunit protein complex, is located thylakoid membrane of plants and other photosynthetic organisms. The complex absorbs the photons of light to capture the electrons which are then transferred to plastoquinone (Krivanek et al, 2007). It is shown that beta carotene is involved in photosystem II (Ferreira et al, 2004;Telfer 2005;Krivanek et al, 2007).…”

“…The complex absorbs the photons of light to capture the electrons which are then transferred to plastoquinone (Krivanek et al, 2007). It is shown that beta carotene is involved in photosystem II (Ferreira et al, 2004;Telfer 2005;Krivanek et al, 2007). It can thus be expected an interaction between LYCs and photosystem II protein.…”