ATP-binding cassette transporters in Lactococcus lactis. (a) The oligopeptide transport system (Opp) uptakes peptides that have been processed by PrtP OppA binds the peptide and donates it to the translocator complex of Opp in the membrane. (b) The multidrug transporter LmrA functions as a homologous dimer. Antimicrobial drugs are picked up in the inner leaflet and extruded in a medium. (c) The glycine-betaine-uptake system is activated by hyperosmotic stress. The glycine-betaine-binding domain opuABC) is linked to the translocator domain and the ABC-binding cassette domain (OnuAA).