Photosystem II: Difference between revisions

This structure of '''Photosystem II''' was crystallized from the cyanobacteria, ''Thermosynechococcus elongatus'', at 3.0Å <ref>PMID: 16355230</ref> and at 3.50 Å <ref name="Archit">PMID: 14764885</ref>. PDB codes are [[2axt]] and [[1s5l]], respectively.  Cyanobacteria and plants both contain Photosystem II while photosynthetic bacteria contain the bacterial reaction center.  This photosynthetic protein complex is associated with a variety of functional ligands. It is a <scene name='Photosystem_II/Psii_dimer/1'>dimer</scene> composed mainly of alpha-helices.  Nineteen <scene name='Photosystem_II/Protein_only/1'>subunits</scene> are in each monomer, with multiple extrinsic subunits associated with the oxygen evolving complex missing from this crystallization.  Photosystem II is a membrane bound protein complex that in plants is associated with the thylakoid membrane of chloroplasts.  <scene name='Photosystem_II/Hydrophobic_polar/1'>Polar and hydrophobic</scene> regions correlate with membrane associated nature of the protein.  '''<span style="color:gray;background-color:black;font-weight:bold;">Hydrophobic</span>''' helices make up the transmembranal portion, while '''<FONT COLOR="#C031C7">polar</FONT>''' residues are concentrated externally on either side of the membrane.

Another important facet of Photosystem II is its ability to oxidize water to oxygen with its <scene name='Photosystem_II/Oxygen_evolving_centers/11'>oxygen evolving centers</scene>.  These centers are <scene name='Photosystem_II/Single_oxygen_evolving/1'>cubane-like</scene> structures with 3 '''<FONT COLOR="#8D38C9">manganese</FONT>''', 4 '''<FONT COLOR="#C11B17">oxygen</FONT>''' and a '''<span style="color:lime;background-color:black;font-weight:bold;">calcium</span>''' linked to a fourth manganese<ref name="Archit" />.  Oxidation of water leaves 2 H ⁺ on the lumenal side of the membrane, helping to establish the proton gradient essential for ATP synthesis in the CF₁CF₀-ATP sythase protein.