Cyanobacterial photosystem II at 2.9-Å resolution and the role of quinones, lipids, channels and chloride

Abstract

Photosystem II (PSII) is a large homodimeric protein-cofactor complex located in the photosynthetic thylakoid membrane that acts as light-driven water:plastoquinone oxidoreductase. The crystal structure of PSII from Thermosynechococcus elongatus at 2.9-A resolution allowed the unambiguous assignment of all 20 protein subunits and complete modeling of all 35 chlorophyll a molecules and 12 carotenoid molecules, 25 integral lipids and 1 chloride ion per monomer. The presence of a third plastoquinone Q(C) and a second plastoquinone-transfer channel, which were not observed before, suggests mechanisms for plastoquinol-plastoquinone exchange, and we calculated other possible water or dioxygen and proton channels. Putative oxygen positions obtained from a Xenon derivative indicate a role for lipids in oxygen diffusion to the cytoplasmic side of PSII. The chloride position suggests a role in proton-transfer reactions because it is bound through a putative water molecule to the Mn(4)Ca cluster at a distance of 6.5 A and is close to two possible proton channels.

Nanodomains of Cytochromeb 6 fand Photosystem II Complexes in Spinach Grana Thylakoid Membranes

“…AFM images of the three grana preparations recorded under liquid revealed appressed double membranes 400 to 500 nm in diameter and 18 to 20 nm in height. The grana membranes are covered with topographic features protruding 3 to 5 nm from the surrounding membrane surface that are 16 to 20 nm in width, consistent with the structure of the lumenal protrusions of the PSII core complex (Zouni et al, 2001;Ferreira et al, 2004;Loll et al, 2005;Guskov et al, 2009;Umena et al, 2011;Sznee et al, 2011) (Figures 1A to 1C). The holes and frayed edges often evident in aG membranes ( Figure 1A) suggested a level of damage, as observed previously (van Roon et al, 2000;Sznee et al, 2011).…”

Photosystem II: The Water-Splitting Enzyme of Photosynthesis

“…All of the small subunits have a single transmembrane helix except for PsbZ, which has two (see Table 1). Subsequent X-ray models of cyanobacterial PSII by Loll et al (2005), Guskov et al (2009), and Umena et al (2011) agreed with the assignments of the small subunits made by Ferreira et al (2004), with 1.9 Å confirming the location of Ycf12 adjacent to PsbK and PsbZ. The 2.9-Å crystal structure of Guskov et al (2009) contained an additional transmembrane helix assigned to PsbY, but this peripheral subunit was absent in the structures of Ferreira et al (2004) and Umena et al (2011).…”

“…This quinone/quinol diffusion channel exits between the subunits of Cyt b559 and PsbJ and is coated with the phytol chains of several Chls and acyl chains of lipids as well as the close proximity of two carotenoids, thus imposing a high degree of lipophylicity. A second potential quinone channel has been postulated that is based on the assignment of a third PQ molecule in the 2.9-Å PSII structure refined by Guskov et al (2009). However, this additional PQ molecule was not identified in the 1.9-Å structure of Umena et al (2011).…”

Structural organization of an intact phycobilisome and its association with photosystem II

“…We screened these particles and obtained a 3D reconstruction, in which we can observe a clear density with a volume in agreement with the size of a PSII dimer ( Figure 1E and Supplementary information, Figure S5B). To test whether the density is contributed by PSII, we first performed an immunoblotting experiment, which showed that the PBS sample contained the reaction center subunits (D1 and D2) of PSII [33,34] but no PsaA (a PSI protein) or PsbO (a PSII peripheral protein required for normal oxygen evolution) ( Figure 1G). Second, we performed immunogold labelling experiments using antibody against D1 and observed gold particle labelling at the bottom of the PBS, which is consistent with the assignment of the density as PSII ( Figure 1H).…”