Fig. 1: MdtF regulation and structural features.

A mdtEF expression is regulated by the two-component system EvgAS, a signal transduction system that confers acid resistance to E. coli. mdtEF expression was also purported to be controlled by the conserved alternative sigma factor RpoS, required for E. coli survival in stress conditions associated with starvation, such as osmotic challenges, heat shock, and oxidative stress. In addition, the upregulation of mdtEF, accompanied by increased efflux activity and drug tolerance, is observed in anaerobically grown E. coli. During this condition, the upregulation of mdtEF is induced by the global anaerobic regulatory factor ArcA, which controls the expression of genes related to the shift in the mode of energy metabolism from aerobic to anaerobic. B Structure of apo-MdtF^WT purified in SMALPs solved by cryo-EM to a resolution of 3.56 Å, demonstrating the maintenance of the native lipid belt encompassing the transmembrane domain of the protein in the electron density map. C Ordered lipids buttressing the transmembrane domain of the three protomers of MdtF can be observed as elongated density in the cryo-EM structure. These were modelled in as PE lipids. D Domains and subdomains of MdtF. E Top view of the periplasmic porter domain, demonstrating its asymmetric structure with open clefts observed within the access and binding states. F Putative substrate translocation channels of MdtF^WT as calculated by MOLE¹⁰⁶.