Structure
The core of PSII consists of a pseudo-symmetric heterodimer of two homologous proteins D1 and D2. Unlike the reaction centers of all other photosystems which have a special pair of closely spaced chlorophyll molecules, the pigment that undergoes the initial photoinduced charge separation in PSII is a chlorophyll monomer. Because the positive charge is not shared across two molecules, the ionised pigment is highly oxidizing and can take part in the splitting of water.
Photosystem II (of cyanobacteria and green plants) is composed of around 20 subunits(depending on the organism) as well as other accessory, light-harvesting proteins. Each photosystem II contains at least 99 cofactors: 35 chlorophyll a, 12 beta-carotene, two pheophytin, two plastoquinone, two heme, one bicarbonate, 20 lipid, the Mn4CaO5 cluster (including chloride ion), and one non heme Fe2+ and two putative Ca2+ ion per monomer. There are different crystal structures of photosystem II. The PDB accession codes for this protein are 3ARC,3BZ1, 3BZ2(3BZ1 and 3BZ2 are monomeric structures of the Photosystem II dimer) 2AXT, 1S5L, 1W5C, 1ILX, 1FE1, 1IZL.
| Photosystem II Light Harvesting complex protein | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | PSII | ||||||||
| Pfam | PF00421 | ||||||||
| InterPro | IPR000932 | ||||||||
| TCDB | 3.E.2 | ||||||||
| OPM superfamily | 2 | ||||||||
| OPM protein | 3arc | ||||||||
|
|||||||||
| Protein Subunits (only with known function) | |
|---|---|
| Subunit | Function |
| D1 | Reaction center Protein, binds Chlorophyll P680, pheophytin, beta-carotene,quinone and manganese center |
| D2 | Reaction center Protein |
| CP43 | Binds manganese center |
| CP47 | |
| PsbO | Manganese Stabilizing Protein |
| Coenzymes/Cofactors | |
| Molecule | Function |
| Chlorophyll | Absorbs light |
| Beta-Carotene | quench excess photoexcitation energy |
| Heme b559 | also Protoporphyrin IX containing iron |
| Pheophytin | Primary electron acceptor |
| Plastoquinone | Mobile intra-thylakoid membrane electron carrier |
| Manganese center | also known as the oxygen evolving center, or OEC |
Read more about this topic: Photosystem II
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