Stabilizes the manganese cluster which is the primary site of water splitting. Associated with the photosystem II complex. On the 2D-gel the determined pI of this protein is: 5.7, its MW is: 35.1 kDa. Belongs to the PsbO family. The order of the peptides shown is unknown. This sequence was originally thought to contain an additional peptide (PubMed:16529377). However, it was later shown that the peptide is likely to be human type II keratin, a common contaminant in proteomic analyses, so it has been removed and the remaining sequence may also contain further contaminations (PubMed:23895828).