Fig. 1.

Overall structure of the BceAB complex. (A) Diagram depicting the organization and predicted membrane topology of a BceAB-RS bacitracin sensing and resistance module. BceA and BceB interact to form a complete ABC transporter complex. BceA subunits in the cytoplasm are colored cyan, and the TM helices and extracellular loop of BceB are colored blue, green, and orange. The BceAB transporter forms a complex with the BceS sensor kinase (dark gray). Conformational cycling of BceAB in response to recognition of bacitracin–UPP complexes initiates autophosphorylation of the BceS sensor kinase, which then phosphorylates (purple star with white P) the BceR response regulator (RR, light gray). Phosphorylated BceR binds to the P_bce promoter and up-regulates expression of the genes encoding the BceAB transporter. (B) Organization of BceRSAB genes in B. subtilis. BceR and BceS are constitutively expressed, whereas BceA and Bce B are controlled by the P_bce promoter that is up-regulated in response to phosphorylated BceR binding. (C) Cryo-EM structure of BceAB in a nucleotide-free conformation. BceA and BceB subunits are colored the same as depicted in (A). The detergent micelle is shown as a transparent gray outline.