Multidrug efflux pumps play a major role in inferring resistance to a broad range of antimicrobial agents to gram-negative bacteria. Multidrug efflux pumps belonging to the RND (Resistance-Nodulation-cell Division) superfamily of transporters are at the core of the antibiotic resistance of Pseudomonas aeruginosa, a notorious nosocomial human pathogen. Our current study focuses on the multidrug efflux pump TriABC from Pseudomonas aeruginosa.
Pseudomonas aeruginosa TriABC complex comprises three subunits: the RND transporter TriC and two distinct periplasmic membrane fusion proteins (MFPs) TriA and TriB. Together with the outer membrane channel OpmH, the pump forms a trans-envelope efflux pump spanning the two membranes and the periplasm of P. aeruginosa cell envelope. TriABC has a narrow substrate and antagonistic specificity with an antimicrobial agent triclosan and a detergent SDS as the only known substrates of this pump. Here, we determined the structure of the TriAxBC by single particle cryo-electron microscopy to 4.3 Å resolution.
We will present this structure. Our results provide evidence for a substrate-free open conformation of TriABC, which represents an intermediate step in the assembly of the efflux complex prior to engagement of the outer membrane channel. We will also discuss our structural analysis that identifies and characterizes the flexibility of the MFPs in absence of its outer membrane channel, in a state characteristic of drug sweeping. We will present the identified two disjoint tunnel networks in TriABC impeding substrate efflux consistent with inhibition of the complex in the unengaged state. This is critical information to fully understand the function and assembly of multidrug efflux pumps and thus, for the development of novel antibiotics strategies.