Using a molecular field theory with atomistic modelling, we provide a complete description of the elastic and flexoelectric properties of the nematic phase formed by liquid crystal dimers which, depending on the parity of the number of atoms in the spacer, have either a bent (odd) or a straight (even) average shape. We can then estimate the flexoelastic ratio and make a direct comparison with the outcome of flexoelectro-optic measurements. Our results demonstrate the extreme sensitivity of the bend elasticity and flexoelectricity to the molecular structure, with dramatic differences between even and odd dimers. An unusually low bend elastic constant is predicted for the latter; we discuss the implications of this result for the high flexoelastic response and the existence of Blue Phases stable over a wide temperature range, which were both recently claimed for odd liquid crystal dimers

The tripartite multidrug efflux system MexAB-OprM is a major actor in Pseudomonas aeruginosa antibiotic resistance by exporting a large variety of antimicrobial compounds. Crystal structures of MexB and of its Escherichia coli homolog AcrB had revealed asymmetric trimers depicting a directional drug pathway by a conformational interconversion (from Loose and Tight binding pockets to Open gate (LTO) for drug exit). It remains unclear how MexB acquires its LTO form. Here by performing functional and cryo-EM structural investigations of MexB at various stages of the assembly process, we unveil that MexB inserted in lipid membrane is not set for active transport because it displays an inactive LTC form with a Closed exit gate. In the tripartite complex, OprM and MexA form a corset-like platform that converts MexB into the active form. Our findings shed new light on the resistance nodulation cell division (RND) cognate partners which act as allosteric factors eliciting the functional drug extrusion.

We analyze the capacity of normal modes to predict observed protein conformational changes, and, notably, those induced by the formation of protein-protein complexes. We show that normal modes calculated in internal coordinate space (ICS) provide better predictions. For a large test set, using the ICS approach describes the conformational changes more completely, and with fewer low-frequency modes than the equivalent Cartesian coordinate modes, despite the fact that the internal coordinate calculations were restricted to torsional angles. This can be attributed to the fact that the use of ICS extends the range over which movements along the corresponding eigenvectors remain close to the true conformational energy hypersurface. We also show that the PaLaCe coarse-grain protein model performs better than a simple elastic network model. We apply ICS normal-mode analysis to protein complexes and, by extending the approach of Sunada and Go̅, [Sunada, S.; Go̅, N. J. Comput. Chem. 1995, 16, 328-336], we show that we can couple an accurate view of the Cartesian coordinate movements induced by ICS modes with the detection of the key residues responsible for the movements.