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Photosystem II
Exploring the Structure
The oxygen-evolving center of photosystem II is a complicated cluster of manganese ions (magenta), calcium (blue green) and oxygen atoms (red). It grips two water molecules and removes four electrons, forming oxygen gas and four hydrogen ions. The actual binding site of the two water molecules is not known for certain, but in the PDB structure 1s5l a bicarbonate ion is bound to the cluster, providing a clue for location of the active site. The picture shows two oxygen atoms from this ion (colored blue): one is bound to a manganese ion, the other is bound to the calcium ion. Notice that the oxygen-evolving center is surrounded by histidines, aspartates and glutamates, which hold it in place. The tyrosine shown in the middle forms a perfect bridge between the water site and the light-capturing chlorophyll.This picture was created with RasMol. You can create similar pictures by clicking on the accession codes here, and picking one of the options under View Structure. When you go to explore this fascinating molecule, be prepared for a challenge. It is very complex and you will need to spend some time to make sense of it. If you want to look at just the reaction center, try displaying non-protein residue numbers 1-8, 40, and 41, along with tyrosine 161 of chain A.
A list of all photosystem II structures in the PDB as of November, 2004 is available here. For more information on photosystem II, click here. To learn about photosystem II from a genomic perspective, take a look at the Protein of the Month at the European Bioinformatics Institute.
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Last changed by: A.Honegger,