Part of the oxygen-evolving complex associated with photosystem II (PSII). PSII is a light-driven water plastoquinone oxidoreductase, using light energy to abstract electrons from H(2)O, generating a proton gradient subsequently used for ATP formation. PSII binds multiple chlorophylls, carotenoids and specific lipids. The cyanobacterial oxygen-evolving complex is composed of PsbO, PsbP, PsbQ, PsbV and PsbU. PsbP and PsbQ are not seen in the crystal structures; however there is biochemical evidence that they are part of the OEC (By similarity). Cyanobacterial PSII is composed of 1 copy each of membrane proteins PsbA, PsbB, PsbC, PsbD, PsbE, PsbF, PsbH, PsbI, PsbJ, PsbK, PsbL, PsbM, PsbT, PsbX, PsbY, PsbZ, Ycf12, 3 peripheral proteins PsbO, PsbU, PsbV and a large number of cofactors. It forms dimeric complexes. Associated with PSII on the lumenal side of the thylakoid membrane. Belongs to the PsbO family.