| 2. |
- Yakushevska, A. E., et al.
(författare)
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The structure of photosystem II in Arabidopsis : localization of the CP26 and CP29 antenna complexes
- 2003
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 42:3, s. 608-613
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Tidskriftsartikel (refereegranskat)abstract
- A genetic approach has been adopted to investigate the organization of the light-harvesting proteins in the photosystem II (PSII) complex in plants. PSII membrane fragments were prepared from wild-type Arabidopis thaliana and plants expressing antisense constructs to Lhcb4 and Lhcb5 genes, lacking CP29 and CP26, respectively (Andersson et al. (2001) Plant Cell 13, 1193-1204). Ordered PSII arrays and PSII supercomplexes were isolated from the membranes of plants lacking CP26 but could not be prepared from those lacking CP29. Membranes and supercomplexes lacking CP26 were less stable than those prepared from the wild type. Transmission electron microscopy aided by single-particle image analysis was applied to the ordered arrays and the isolated PSII complexes. The difference between the images obtained from wild type and antisense plants showed the location of CP26 to be near CP43 and one of the light-harvesting complex trimers. Therefore, the location of the CP26 within PSII was directly established for the first time, and the location of the CP29 complex was determined by elimination. Alterations in the packing of the PSII complexes in the thylakoid membrane also resulted from the absence of CP26. The minor light-harvesting complexes each have a unique location and important roles in the stabilization of the oligomeric PSII structure.
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| 3. |
- Hankamer, B, et al.
(författare)
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Isolation and biochemical characterisation of monomeric and dimeric photosystem II complexes from spinach and their relevance to the organisation of photosystem II in vivo
- 1997
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Ingår i: European Journal of Biochemistry. - 0014-2956 .- 1432-1033. ; 243:1-2, s. 422-429
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Tidskriftsartikel (refereegranskat)abstract
- Membranes enriched in photosystem II were isolated from spinach and further solubilised using n-octyl beta-D-glucopyranoside (OctGlc) and n-dodecyl beta-D-maltoside (DodGlc(2)). The OctGlc preparation had high rates of oxygen evolution and when subjected to size-exclusion HPLC and sucrose density gradient centrifugation, in the presence of DodGlc(2), separated into dimeric (430 kDa), monomeric (236 kDa) photosystem II cores and a fraction containing photosystem II light-harvesting complex (Lhcb) proteins. The dimeric core fraction was more stable, contained higher levels of chlorophyll, beta-carotene and plastoquinone per photosystem II reaction centre and had a higher oxygen-evolving activity than the monomeric cores. Their subunit composition was similar (CP43, CP47, D1, D2, cytochrome b 559 and several lower-molecular-mass components) except that the level of 33-kDa extrinsic protein was lower in the monomeric fraction. Direct solubilisation of photosystem-II-enriched membranes with DodGlc(2), followed by sucrose density gradient centrifugation, yielded a super complex (700 kDa) containing the dimeric form of the photosystem II core and Lhcb proteins: Lhcb1, Lhcb2, Lhcb4 (CP29), and Lhcb5 (CP26). Like the dimeric and monomeric photosystem II core complexes, the photosystem II-LHCII complex had lost the 23-kDa and 17-kDa extrinsic proteins, but maintained the 33-kDa protein and the ability to evolve oxygen. It is suggested, with a proposed model, that the isolated photosystem II-LHCII super complex represents an in vivo organisation that can sometimes form a lattice in granal membranes of the type detected by freeze-etch electron microscopy [Seibert, M., DeWit, M. & Staehelin, L. A. (1987) J. Cell Biol. 105, 2257-2265].
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