Probably part of the ABC transporter complex RfuABCD involved in riboflavin import. Binds riboflavin. Monomer in solution (PubMed:23404400). The complex is probably composed of two ATP-binding proteins (RfuB), two transmembrane proteins (RfuC and RfuD) and a solute-binding protein (RfuA) (Probable). Belongs to the BMP lipoprotein family.