Plays an important role in protecting the acceptor side of photosystem II (PSII) against oxidative damage, especially under iron-limiting growth conditions. May also be part of a periplasmic ABC transporter complex involved in iron import. By iron limitation and to a smaller extent by manganese limitation. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven. Belongs to the bacterial solute-binding protein 1 family.