title: Substrate-dependent dynamics of the multidrug efflux transporter AcrB of Escherichia coli.
abstract: The resistance-nodulation-cell division (RND)-type xenobiotic efflux system plays a major role in the multidrug resistance of gram-negative bacteria. The only constitutively expressed RND system of Escherichia coli consists of the inner membrane transporter AcrB, the membrane fusion protein AcrA, and the outer membrane channel TolC. The latter two components are shared with another RND-type transporter AcrD, whose expression is induced by environmental stimuli. Here, we demonstrate how RND-type ternary complexes, which span two membranes and the cell wall, form in vivo. Total internal reflection fluorescence (TIRF) microscopy revealed that most fluorescent foci formed by AcrB fused to green fluorescent protein (GFP) were stationary in the presence of TolC but showed lateral displacements when tolC was deleted. The fraction of stationary AcrB-GFP foci decreased with increasing levels of AcrD. We propose that the AcrB-containing complex becomes unstable upon the induction of AcrD, which presumably replaces AcrB, a process we call "transporter exchange." This instability is suppressed by AcrB-specific substrates, suggesting that the ternary complex is stabilised when it is in action. These results suggest that the assembly of the RND-type efflux system is dynamically regulated in response to external stimuli, shedding new light on the adaptive antibiotic resistance of bacteria.
authors.affiliation: Department of Frontier Bioscience, Hosei University, Kajino-cho, Koganei, Tokyo 184-8584.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Department of Frontier Bioscience, Hosei University, Kajino-cho, Koganei, Tokyo 184-8584.
authors.forename: Rei
authors.initials: R
authors.lastname: Tamai
authors.affiliation: Department of Frontier Bioscience, Hosei University, Kajino-cho, Koganei, Tokyo 184-8584.
authors.forename: Megumi
authors.initials: M
authors.lastname: Yamazaki
authors.affiliation: Research Center for Micro-Nano Technology, Hosei University, Midori-cho, Koganei, Tokyo 184-0003, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Inaba
authors.affiliation: Department of Frontier Bioscience, Hosei University, Kajino-cho, Koganei, Tokyo 184-8584.|Research Center for Micro-Nano Technology, Hosei University, Midori-cho, Koganei, Tokyo 184-0003, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sowa
authors.affiliation: Department of Frontier Bioscience, Hosei University, Kajino-cho, Koganei, Tokyo 184-8584.|Research Center for Micro-Nano Technology, Hosei University, Midori-cho, Koganei, Tokyo 184-0003, Japan.
authors.forename: Ikuro
authors.initials: I
authors.lastname: Kawagishi
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D018432:Drug Resistance, Multiple; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes; D055550:Protein Stability
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D046912:Multiprotein Complexes; C083496:AcrB protein, E coli; C000588785:AcrD protein, E coli; C073126:tolC protein, E coli