Knock‐out of the chloroplast‐encoded PSI‐J subunit of photosystem I in <i>Nicotiana tabacum</i>

Hansson, Andreas; Amann, Katrin; Zygadlo, Agnieszka; Meurer, Jörg; Scheller, Henrik Vibe; Jensen, Poul Erik

doi:10.1111/j.1742-4658.2007.05722.x

Cited by 17 publications

(10 citation statements)

References 45 publications

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“…Plants lacking PsaF retained an intact antenna complex, however they were severely affected in energy transfer from LHCI (63). ⌬psaJ tobacco plants showed impaired antenna binding and excitation transfer to the PSI core, whereas the functional size of the antenna was not affected (64,65). Our structure agrees with these studies, suggesting that PsaF and PsaJ were optimized for the interactions with LHCI, although they are probably not crucial for the assembly of the antenna onto the core of PSI.…”

Section: Resultssupporting

confidence: 81%

Structure Determination and Improved Model of Plant Photosystem I

Amunts¹,

Toporik²,

Borovikova

et al. 2010

Journal of Biological Chemistry

263

241

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Photosystem I functions as a sunlight energy converter, catalyzing one of the initial steps in driving oxygenic photosynthesis in cyanobacteria, algae, and higher plants. Functionally, Photosystem I captures sunlight and transfers the excitation energy through an intricate and precisely organized antenna system, consisting of a pigment network, to the center of the molecule, where it is used in the transmembrane electron transfer reaction. Our current understanding of the sophisticated mechanisms underlying these processes has profited greatly from elucidation of the crystal structures of the Photosystem I complex. In this report, we describe the developments that ultimately led to enhanced structural information of plant Photosystem I. In addition, we report an improved crystallographic model at 3.3-Å resolution, which allows analysis of the structure in more detail. An improved electron density map yielded identification and tracing of subunit PsaK. The location of an additional ten ␤-carotenes as well as five chlorophylls and several loop regions, which were previously uninterpretable, are now modeled. This represents the most complete plant Photosystem I structure obtained thus far, revealing the locations of and interactions among 17 protein subunits and 193 non-covalently bound photochemical cofactors. Using the new crystal structure, we examine the network of contacts among the protein subunits from the structural perspective, which provide the basis for elucidating the functional organization of the complex.During oxygenic photosynthesis, solar energy is converted into chemical energy for all higher forms of life on Earth. This process is driven by a photosynthetic apparatus within the thylakoid membranes of cyanobacteria, algae, and plants. The photochemical functions are performed by two photosystems: Photosystems I (PSI) and II (PSII). 4 These photosystems are multisubunit complexes that consist of protein and non-protein components, and drive light-dependent electron transfer reactions, resulting in the formation of high energy products: ATP and NADPH (1, 2). PSII catalyzes light-driven oxidation of water, providing electrons to PSI via the plastoquinone pool, the cytochrome b 6 f complex, and the water-soluble electron carrier plastocyanin. This electron transfer is coupled to the increase of a transmembrane electrochemical potential gradient (proton motive force), which powers ATP-synthase for phosphorylation of ADP to ATP. PSI catalyzes light-driven electron transport from plastocyanin at the inner face of the membrane (lumen) to ferredoxin on the outside of the membrane (stroma). The reduced ferredoxin is subsequently used for NADPH production, which provides the reducing power for the conversion of carbon dioxide to organic molecules. Although PSII is unique in its ability to extract electrons from water, PSI is arguably the most efficient photoelectric apparatus in nature, exhibiting a quantum efficiency of almost 100% in its utilization of light for electron transport (3). The ability of PS to...

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Section: Resultssupporting

confidence: 81%

Structure Determination and Improved Model of Plant Photosystem I

Amunts¹,

Toporik²,

Borovikova

et al. 2010

Journal of Biological Chemistry

263

241

View full text Add to dashboard Cite

show abstract

“…Because PsaF and PsaJ have one transmembrane helix and are located between the PSI core and LHCI, it is likely that PsaF and PsaJ are integrated before the LHCI attaches to the PSI subcomplex. The absence of PsaF and PsaJ, however, does not significantly affect the LHCI attachment (42)(43)(44).…”

Section: Integration Of Psag and Psak Is The Latest Assemblymentioning

confidence: 87%

Identification and Characterization of an Assembly Intermediate Subcomplex of Photosystem I in the Green Alga Chlamydomonas reinhardtii

Ozawa

Onishi

Takahashi

2010

Journal of Biological Chemistry

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Photosystem I (PSI) is a multiprotein complex consisting of the PSI core and peripheral light-harvesting complex I (LHCI) that together form the PSI-LHCI supercomplex in algae and higher plants. The supercomplex is synthesized in steps during which 12-15 core and 4 -9 LHCI subunits are assembled. Here we report the isolation of a PSI subcomplex that separated on a sucrose density gradient from the thylakoid membranes isolated from logarithmic growth phase cells of the green alga Chlamydomonas reinhardtii. Pulse-chase labeling of total cellular proteins revealed that the subcomplex was synthesized de novo within 1 min and was converted to the mature PSI-LHCI during the 2-h chase period, indicating that the subcomplex was an assembly intermediate. The subcomplex was functional; it photooxidized P700 and demonstrated electron transfer activity. The subcomplex lacked PsaK and PsaG, however, and it bound PsaF and PsaJ weakly and was not associated with LHCI. It seemed likely that LHCI had been integrated into the subcomplex unstably and was dissociated during solubilization and/or fractionation. We, thus, infer that PsaK and PsaG stabilize the association between PSI core and LHCI complexes and that PsaK and PsaG bind to the PSI core complex after the integration of LHCI in one of the last steps of PSI complex assembly.

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“…Different from the situation in Chlamydomonas, tobacco psaJ mutants generated by stable transformation of the chloroplast genome show a slightly retarded growth and suffer from an up to 30% reduction in PSI contents (Hansson et al, 2007;Schöttler et al, 2007). It is not yet clear whether the reduced PSI accumulation is due to impaired assembly or decreased stability of PSI.…”

Section: Psajmentioning

confidence: 94%