Part of an ABC transporter complex that transports riboflavin into the cell (PubMed:25938806). Binds riboflavin (PubMed:25345570). The complex is likely composed of an ATP-binding protein, a transmembrane protein (RibX) and a solute-binding protein (RibY). Expression is probably regulated by riboflavin, via an FMN riboswitch. Belongs to the NMT1 family.