Part of the ABC transporter DppABCDF involved in dipeptide transport (PubMed:7536291). Responsible for the translocation of the substrate across the membrane (Probable). When a foreign outer membrane heme receptor is expressed in E.coli, DppABCDF can also transport heme and its precursor, 5-aminolevulinic acid (ALA), from the periplasm into the cytoplasm. The complex is composed of two ATP-binding proteins (DppD and DppF), two transmembrane proteins (DppB and DppC) and a solute-binding protein (DppA) (PubMed:7536291, PubMed:16905647). MppA can replace DppA as binding protein for heme and ALA transport (PubMed:16905647). Inactivation of the gene abolishes use of heme as an iron source. Belongs to the binding-protein-dependent transport system permease family. OppBC subfamily.