New OprM structure highlighting the nature of the N-terminal anchor.

Among the different mechanisms used by bacteria to resist antibiotics, active efflux plays a major role. In Gram-negative bacteria, active efflux is carried out by tripartite efflux pumps that form a macromolecular assembly spanning both membranes of the cellular wall. At the outer membrane level, a well-conserved outer membrane factor (OMF) protein acts as an exit duct, but its sequence varies greatly among different species.

Stoichiometry of the MexA-OprM binding, as investigated by blue native gel electrophoresis.

Multidrug resistance has become a serious concern in the treatment of bacterial infections. A prominent role is ascribed to the active efflux of xenobiotics out of the bacteria by a tripartite protein machinery. The mechanism of drug extrusion is rather well understood, thanks to the X-ray structures obtained for the Escherichia coli TolC/AcrA/AcrB model system and the related Pseudomonas aeruginosa OprM/MexA/MexB.

Structure of reconstituted bacterial membrane efflux pump by cryo-electron tomography.

Complexes of OprM and MexA, two proteins of the MexA-MexB-OprM multidrug efflux pump from Pseudomonas aeruginosa, an opportunistic Gram-negative bacterium, were reconstituted into proteoliposomes by detergent removal. Stacks of protein layers with a constant height of 21nm, separated by lipid bilayers, were obtained at stoichiometry of 1:1 (w/w). Using cryo-electron microscopy and tomography, we showed that these protein layers were composed of MexA-OprM complexes self-assembled into regular arrays.

Structural and dynamical insights into the opening mechanism of P. aeruginosa OprM channel.

Originally described in bacteria, drug transporters are now recognized as major determinants in antibiotics resistance. For Gram-negative bacteria, the reversible assembly consisting of an inner membrane protein responsible for the active transport, a periplasmic protein, and an exit outer membrane channel achieves transport. The opening of the outer membrane protein OprM from Pseudomonas aeruginosa was modeled through normal mode analysis starting from a new X-ray structure solved at 2.

Tracking membrane protein association in model membranes.

Membrane proteins are essential in the exchange processes of cells. In spite of great breakthrough in soluble proteins studies, membrane proteins structures, functions and interactions are still a challenge because of the difficulties related to their hydrophobic properties. Most of the experiments are performed with detergent-solubilized membrane proteins.