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. Regulated by IdiB. May also be indirectly regulated by DpsA and Fur. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has not been experimentally proven. Belongs to the bacterial solute-binding protein 1 family.