Supramolecular organization of photosystem II and its light‐harvesting antenna in partially solubilized photosystem II membranes

Abstract

We present an extended analysis of the organization of green plant photosystem II and its associated lightharvesting antenna using electron microscopy and image analysis. The analysis is based on a large dataset of 16 600 projections of negatively stained PSII±LHCII supercomplexes and megacomplexes prepared by means of three different pretreatments. In addition to our previous work on this system [Boekema, E.J., van Roon, H., Calkoen, F., Bassi, R. and Dekker, J.P. (1999) Biochemistry 38, 2233±2239], the following results were obtained.The rotational orientation of trimeric LHCII at the S, M and L binding positions was determined. It was found that compared to the S trimer, the M and L trimers are rotationally shifted by about 2208 and 2508, respectively.The number of projections with empty CP29, CP26 and CP24 binding sites was found to be about 0, 18 and 4%, respectively. We suggest that CP26 and CP24 are not required for the binding of trimeric LHCII at any of the three binding positions.A new type of megacomplex was observed with a characteristic windmill-like shape. This type III megacomplex consists of two C 2 S 2 supercomplexes connected at their CP26 tips.Structural variation in the region of the central dimeric photosystem II complex was found to occur at one specific position near the periphery of the complex. We attribute this variation to the partial absence of an extrinsic polypeptide or one or more small intrinsic membrane proteins.Keywords: photosystem II; light harvesting complex; thylakoid membrane; electron microscopy.A key role in the energy-conserving mechanisms of green plants is played by photosystem II (PSII). Its major task is to use light energy for the reduction of plastoquinone, the oxidation of water and the formation of a transmembrane pH gradient. It consists of at least 25 different types of protein subunits [1], which are organized into two structurally and functionally distinct parts. The first part is the core complex, a well-defined structure that is responsible for all electron transfer reactions in PSII, including the formation of oxygen. It contains the reaction centre proteins D1 and D2, cytochrome b-559, two core antenna proteins called CP47 and CP43, a number of extrinsic proteins indirectly involved in the oxygenevolving process, and several small proteins of unknown function [1]. There is overwhelming evidence that the PSII core complex is organized as a dimer in the stacked, appressed regions of the thylakoid membrane [2±4]. The structure of the PSII core complex without the CP43 subunit has been determined at 8 A Ê resolution by electron crystallography on two-dimensional crystals [5,6]. The structure reveals 23 transmembrane a-helices [7], of which six have been assigned to CP47, and 10 to the D1 and D2 proteins. Two of the remaining seven transmembrane a-helices are probably formed by cytochrome b-559, while the others are thought to belong to small proteins consisting of a single transmembrane a-helix [6].The second part of PSII is the peripheral antenna, which in g...

Characterization and Evolution of Tetrameric Photosystem I from the Thermophilic Cyanobacterium Chroococcidiopsis sp TS-821

“…Imaging and image processing were performed as described in previous studies (Oostergetel et al, 1998;Boekema et al, 1999;Watanabe et al, 2014). For the final class sums, the best 10% of the projections were summed.…”

Minor Antenna Proteins CP24 and CP26 Affect the Interactions between Photosystem II Subunits and the Electron Transport Rate in Grana Membranes of Arabidopsis

“…LHCII is the major component of the outer antenna and comprises different heterotrimers of LHCB1, LHCB2, and LHCB3 gene products, while minor antenna complexes (Chlorophyll Protein 29 [CP29], CP26, and CP24) are encoded by LHCB4, LHCB5, and LHCB6 genes, respectively, and are found as monomers (Bassi et al, 1996;Jansson, 1999). Structural analysis of PSII and Lhcb supercomplex organization within grana membranes has revealed that minor complexes CP26 and CP29 are located in between the core complex and the trimeric LHCII (Harrer et al, 1998;Boekema et al, 1999). Additional LHCII trimers, depending on growth light intensity (Dekker and Boekema, 2005;Morosinotto et al, 2006;Ballottari et al, 2007), complete the PSII structure and require CP24 for connection to PSII core by forming a complex with CP29 (Bassi and Dainese, 1992;Yakushevska et al, 2003;Dekker and Boekema, 2005).…”

Phosphorylation of the Lhcb2 isoform of Light Harvesting Complex II is central to state transitions

“…In the stably bound S trimer, Lhcb1 and Lhcb2 are more abundant, whereas the moderately bound M trimer contains mostly Lhcb1 and Lhcb3 (Galka et al, 2012). PSII supercomplexes isolated from spinach (Spinacia oleracea) showed the presence of an extra LHCII trimer (L trimer); therefore, it is possible that, in Arabidopsis, other trimers are associated with the PSII dimer in a more labile supercomplex that cannot be isolated (Boekema et al, 1999). A single LHCII trimer, containing Lhcb1 and Lhcb2, stably associates with PSI to constitute the PSI-LHCII supercomplex, whose formation is dependent on LHCII phosphorylation by STN7 in state 2 (Kouril et al, 2005;Galka et al, 2012).…”