Controls the interaction of photosystem II (PSII) cores with the light-harvesting antenna. Heterodimer of an alpha subunit and a beta subunit. 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. Associated with the photosystem II complex. Belongs to the PsbZ family. Extended N-terminus.