Together with two further proteins McbE and McbG this protein causes immunity to the peptide antibiotic microcin B17, which inhibits DNA replication in enterobacteriaceae. Immunity is determined by two different mechanisms. McbE is involved in the production of extracellular MccB17 and, in a complex with mcbf it also serves as 'pump' for the export of active MccB17 from the cytoplasm to the periplasmic space. Belongs to the ABC transporter superfamily.