3.A.1.122.20
MacAB-MFP complex of 3 subunits involved in the resistance of antibiotics and antimicrobial peptides. Yang et al. 2018 reported the crystal structures of Spr0694-0695 (MacAB) at 3.3 Å and Spr0693 (MFP; TC# 8.A.1) at 3.0 Å resolution, revealing a MacAB-like efflux pump. The dimeric MacAB adopts a non-canonical fold, the transmembrane domain of which consists of a dimer with eight tightly packed TMSs (4 per subunit) with an extracellular domain between the first and second helices, whereas Spr0693 (the MFP) forms a nanotube channel docked onto the ABC transporter. Structural analyses, combined with ATPase activity and antimicrobial susceptibility assays, enabled the proposal of a putative substrate-entrance tunnel with lateral access controlled by a guard helix (Yang et al. 2018).