Involved in the binding and/or turnover of quinones at the Q(B) site of Photosystem II. 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, at least 3 peripheral proteins PsbO, PsbU, PsbV and a large number of cofactors. It forms dimeric complexes. By high-light stress. Cells have about 30% less PSII and a minor uncoupling of the antenna. Belongs to the PsbX family. Type 1 subfamily.