1. Structure of photosystem I at atomic resolution (PS I) 2. Function of PS I 3. Genetic analysis of structure-function relations 4. Two branches in electron transport in PS I 5. PS I a photo-nano-switch PS I is a light driven plastocyanin ferredoxin oxidoreductase. Quantum efficiency for electron transfer is 1 PS I is part of the photosynthetic apparatus. A membrane protein chlorophyll complex one of the 4 complexes that make the transmembrane oxidoreductase system that oxidize water to O 2 and reduces NADP+ to NADPH + H+, pump H+ that drive ATP synthesis.
Composition 12 subunits A-M, X (no H, G), 9 of them are transmembrane peptides. C, D & E are attached at the outside (storma). M.W. 255 kDa 96 Chlorophylls, 22 carotenoids, 2 phylloquinons, 3 [4Fe4S] clusters.
Subunit arragem -ent view from stroma
FeS A/B FeS X Subunit C Subunits A, B
The electron transfer chain is attached on subunits A, B & C. P700, A0, A1, Fx, FA & FB. P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591. A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673. Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster? Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology. FA and FB- 4Fe4S iron sulfur clusters
FeS B FeS A FeS X PQ Ao (CHL) P700 (CHL 2 )
The electron transfer chain is attached on subunits A, B & C. P700, A0, A1, Fx, FA & FB. P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591. A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673. Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster? Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology. FA and FB- 4Fe4S iron sulfur clusters
The electron transfer chain is attached on subunits A, B & C. P700, A0, A1, Fx, FA & FB. P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591. A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673. Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster? Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology. FA and FB- 4Fe4S iron sulfur clusters
The electron transfer chain is attached on subunits A, B & C. P700, A0, A1, Fx, FA & FB. P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591. A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673. Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster? Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology. FA and FB- 4Fe4S iron sulfur clusters