3.A.1.134.3
The bacitracin exporter, BceAB (BarAB; YtsCD) (Bernard et al., 2003; Ohki et al., 2003; Rismondo and Schulz 2021).  It functions in both signaling to the two component system, BceRS, and in export of an antimicrobial peptide (Dintner et al. 2014).  BceB interacts directly with BceS, and BceB binds bacitracin (Dintner et al. 2014).  Specific regions and residues are involved in signalling or transport (Kallenberg et al. 2013).  More recent studies suggest that BceAB may cause bacitracin resistance by transferring undecaprenyl pyrophosphate from the exteral to the internal leaflet of the inner membrane where it can't bind bacitracin and other lantibiotics that use Lipid II as a receptor (Draper et al. 2015). It may cause drug detoxification by targeet protection (Rismondo and Schulz 2021).  BceA transports Hoechst 33342, ethidium bromide, doxorubicin and cervimycin C, and the BceAB-BceRS system of B. subtilis is required for the resistance against actagardine, mersacidin and plectasin (Rismondo and Schulz 2021).  Bacitracin blocks the recycling of lipid carriers during the lipid II cycle of cell wall biosynthesis by binding to the diphosphate lipid carrier undecaprenyl pyrophosphate (UPP), and actagardine, mersacidin and plectasin directly bind lipid II. A phylogenetic analysis revealed that BceAB-like transporters are nearly exclusively found in Firmicutes and confer resistance to a subset of antimicrobials. These transporters, belonging to the peptide 7 exporter family, usually consist of two ATP-binding proteins (BceA), a large permease (BceB).  They are mostly associated with a BceRS-like two-component system. Both components, the transporter BceAB and the two-component system BceRS, are required for sensing of and resistance to bacitracin in B. subtilis (Rismondo and Schulz 2021).