1.97.1.12 ? 21000-22000 Da, photosystem 1 subunit PsaF that is involved in the docking of the electron-donor proteins plastocyanin and cytochrome c6, SDS-PAGE 713465 1.97.1.12 dimer in strain TS-821 PSI forms tetrameric, dimeric, and monomeric species, a tetrameric PSI has two PSI dimers associated together with interdimer gaps, while the PSI dimer is composed of two tightly tethered PSI monomers, subunit organization, structure comparisons, overview 746026 1.97.1.12 heterotetramer two-dimensional maps obtained by single particle electron microscopy clearly show that the tetramer lacks four-fold symmetry and is actually composed of a dimer of dimers with C2 symmetry, cryo-electron microscopy is used for 3D reconstruction of the PSI tetramer complex and a 3D model at 11.5 A resolution is obtained. A 2D map within the membrane plane of about 6.1 A is used for modeling, structure model comparison with the PSI structure of Thermosynechococcus elongatus at 2.5 A, PDB ID 1JB0, overview. The PsaL subunit of strain TS-821 is modeled using PsaL subunit of Pisum sativum as a template, PDB ID 4Y28L. The modeled PsaL subunit of TS-821 is used to substitute the existing PsaL subunit in crystal structure of Thermosynechococcus elongatus and most of the subunits from the crystal structure of Thermosynechococcus elongatus are fitted separately into the 3D volumemap of TS-821. Comparison of trimeric interface of Thermosynechococcus elongatus with interface type 1 of TS-821 744411 1.97.1.12 monomer in strain TS-821 PSI forms tetrameric, dimeric, and monomeric species, a tetrameric PSI has two PSI dimers associated together with interdimer gaps, while the PSI dimer is composed of two tightly tethered PSI monomers, subunit organization, structure comparisons, overview 746026 1.97.1.12 monomer inside the trimer, subunits PsaL, PsaI and PsaM (5 alpha-helices in total) are located in the center of the trimerization domain of PSI, thereby forming most of the contacts between the monomers 746500 1.97.1.12 additional information a cyanobacterial PSI monomer consists of 11–12 protein subunits 710876 1.97.1.12 additional information amino acid sequence comparisons 744411 1.97.1.12 additional information plant and algal PSI complexes contain 14-15 protein subunits. Of these, only PsaA, PsaB, and PsaC bind the cofactors of the electron transfer system. PsaA and PsaB form the core complex around which other subunits are organized. The PsaC, PsaD, PsaH, and PsaE proteins form the stromal peripheral domain that contains the terminal electron donors and the ferredoxin-docking site. PsaN of plant and algal PSI is a lumenal peripheral protein. PsaN and the large lumenal domain of PsaF form the plastocyanin docking site of plant and algal PSI. The remaining proteins of PSI are integral membrane proteins with 1–3 transmembrane helices. The function of the PSI proteins 710876 1.97.1.12 additional information PsaE (a peripheral subunit of the PSI complex) is involved in the docking of ferredoxin/flavodoxin to the PSI complex and also participates in the cyclic electron transfer around phosphosystem I. The interactions formed between different subunits of the complex may be hydrophobic or electrostatic in nature 711194 1.97.1.12 additional information the crystal structure reveals the configuration of PsaK, a core subunit important for state transitions in plants, a conserved network of water molecules surrounding the electron transfer centres and an elaborate structure of lipids bridging PSI and its LHCI antenna. The structure of Psak suggests alternative conformations, overview 745870 1.97.1.12 additional information the membrane-embedded core of each PS I monomer is formed by the two largest subunits, PsaA and PsaB, which bind electron transport cofactors arranged in two symmetrical branches, A and B, extending from P700, a pair of chlorophyll a molecules located on the lumenal side, to the [4Fe-4S] cluster FX, placed on the opposite stromal side of the complex 745986 1.97.1.12 additional information the photosystem I reaction center complex is composed of the 83 kDa subunits A and B, and at least six other subunits with molecular mass below 20 kDa 712730 1.97.1.12 additional information the photosystem I reaction center is obtained in two forms, monomeric and trimeric 713434 1.97.1.12 additional information the PSI core complex prepared from cucumber cotyledons contains 80 chlorophylls per reaction center (P700) and eight polypeptides with apparent molecular masses of 65/63, 20,19.5,18.5,17.5,7.6, and 5.8 kDa. The amount of 18.5 kDa polypeptide in the PSI complex affects the activity. When this polypeptide is largely depleted, the complex is almost inactive. The inactivation is due to inhibition of electron transfer from plastocyanin to photooxidized P700. Chemical cross-linking and N-terminal amino acid sequencing experiments indicate that the 18.5-kDa polypeptide is the plastocyanin-docking protein and the psaF gene product 712315 1.97.1.12 tetramer in strain TS-821 PSI forms tetrameric, dimeric, and monomeric species, a tetrameric PSI has two PSI dimers associated together with interdimer gaps, while the PSI dimer is composed of two tightly tethered PSI monomers, subunit organization, structure comparisons, overview 746026 1.97.1.12 trimer - 745987 1.97.1.12 trimer cyanobacterial PSI is usually trimeric 744412 1.97.1.12 trimer inside the trimer, subunits PsaL, PsaI and PsaM (5 alpha-helices in total) are located in the center of the trimerization domain of PSI, thereby forming most of the contacts between the monomers 746500 1.97.1.12 trimer three-dimensional structure analysis using PDB ID 1JB0, overview. Two transmembrane large protein subunits PsaA and PsaB compose C2-symmetrical heterodimeric core complex containing most of the electron transfer cofactors. The electron transfer chain of PS I consists of the primary donor-chlorophyll (Chl) dimer P700, primary acceptor A0 (four Chl molecules), A1 (two phylloquinone molecules), and iron-sulfur clusters FX, FA, and FB.The terminal FA/FB clusters are located on the small extrinsic PsaC subunit 745985