This entry consists of the 23 kDa subunit of oxygen evolving system of photosystem II or PsbP from various plants (where it is encoded by the nuclear genome) and Cyanobacteria (known as CyanoP). The 23 KDa PsbP protein is required for PSII to be fully operational in vivo, it increases the affinity of the water oxidation site for Cl- and provides the conditions required for high affinity binding of Ca2+ [2]. Structure of CyanoP from Synechocystis sp. revealed that it has an alpha-beta-alpha fold containing 10 beta strands organized into two anti-parallel beta-sheets, packed against alpha-helices. This entry covers the first seven beta-stands (beta1-beta7) and the N-terminal alpha-helix [1].

1: Photoactivation and photoinhibition are competing in a mutant of Chlamydomonas reinhardtii lacking the 23-kDa extrinsic subunit of photosystem II. Rova EM, Mc Ewen B, Fredriksson PO, Styring S; J Biol Chem 1996;271:28918-28924. PMID:8910540

2: Nucleotide sequence of the psbP gene encoding precursor of 23-kDa polypeptide of oxygen-evolving complex in Arabidopsis thaliana and its expression in the wild-type and a constitutively photomorphogenic mutant. Kochhar A, Khurana JP, Tyagi AK; DNA Res 1996;3:277-285. PMID:9039496

3: Solution structure of CyanoP from Synechocystis sp. PCC 6803: new insights on the structural basis for functional specialization amongst PsbP family proteins. Jackson SA, Hinds MG, Eaton-Rye JJ; Biochim Biophys Acta. 2012;1817:1331-1338. PMID:22414666

4: Structure of CyanoP at 2.8 A: implications for the evolution and function of the PsbP subunit of photosystem II . Michoux F, Takasaka K, Boehm M, Nixon PJ, Murray JW; Biochemistry. 2010;49:7411-7413. PMID:20698571