Highlights d Cryo-EM analysis of thermostabilized mGlu 5 receptor bound to inhibitors or activators d X-ray structure of trans-Alloswitch-1 bound to thermostable mGlu 5 7TMs d Photopharmacology provides insight into allosteric regulation of mGlu 5 7TMs d Multiple conformations of mGlu 5 receptor activate G protein

Biofilms are organized communities of bacterial cells that are responsible for the majority of human chronic bacterial infections. Providencia stuartii is a Gram-negative biofilm-forming bacterium involved in high incidence of urinary tract infections in catheterized patients. Yet, the structuration of these biofilms, and their resistance to environmental insults remain poorly understood. Here, we report on planktonic cell growth and biofilm formation by P. stuartii, in conditions that mimic its most common pathophysiological habitat in humans, i.e. the urinary tract. We observed that, in the planktonic state, P. stuartii forms floating communities of cells, prior to attachment to a surface and subsequent adoption of the biofilm phenotype. P. stuartii planktonic and biofilm cells are remarkably resistant to calcium, magnesium and to high concentrations of urea, and show the ability to grow over a wide range of pHs. Experiments conducted on a P. stuartii strain knocked-out for the Omp-Pst2 porin sheds light on the role it plays in the early stages of growth, as well as in the adaptation to high concentration of urea and to varying pH.

Highlights d Lipid interactions of PC2 channels have been explored by MD simulation and cryo-EM d PIP 2 binds to a site corresponding to the vanilloid/lipid binding site of TRPV1 d Cholesterol binds between the S3 and S4 helices and S6 of the adjacent subunit d PC2, in common with other channels, may be modulated by PIPs and cholesterol

The role of major porin OmpPst1 of Providencia stuartii in antibiotic susceptibility for two carbapenems is investigated by combining high-resolution conductance measurements, liposome swelling, and microbiological assays. Reconstitution of a single OmpPst1 into a planar lipid bilayer and measuring the ion current, in the presence of imipenem, revealed a concentration-dependent decrease in conductance, whereas meropenem produced well-resolved short ion current blockages. Liposome swelling assays suggested a small flux of imipenem in contrast to a rapid permeation of meropenem. The lower antibiotic susceptibility of P. stuartii to imipenem compared to meropenem correlated well with the decreased level of permeation of the former through the OmpPst1 channel.

The gram-negative pathogen forms floating communities within which adjacent cells are in apparent contact, before depositing as canonical surface-attached biofilms. Because porins are the most abundant proteins in the outer membrane of gram-negative bacteria, we hypothesized that they could be involved in cell-to-cell contact and undertook a structure-function relationship study on the two porins of, Omp-Pst1 and Omp-Pst2. Our crystal structures reveal that these porins can self-associate through their extracellular loops, forming dimers of trimers (DOTs) that could enable cell-to-cell contact within floating communities. Support for this hypothesis was obtained by studying the porin-dependent aggregation of liposomes and model cells. The observation that facing channels are open in the two porin structures suggests that DOTs could not only promote cell-to-cell contact but also contribute to intercellular communication.

The metabotropic glutamate (mGlu) receptors are class C G protein-coupled receptors (GPCRs) that modulate synaptic activity and plasticity throughout the mammalian brain. Signal transduction is initiated by glutamate binding to the venus flytrap domains (VFT), which initiates a conformational change that is transmitted to the conserved heptahelical domains (7TM) and results ultimately in the activation of intracellular G proteins. While both mGlu1 and mGlu5 activate Gαq G-proteins, they also increase intracellular cAMP concentration through an unknown mechanism. To study directly the G protein coupling properties of the human mGlu5 receptor homodimer, we purified the full-length receptor, which required careful optimisation of the expression, N-glycosylation and purification. We successfully purified functional mGlu5 that activated the heterotrimeric G protein Gq. The high-affinity agonist-PAM VU0424465 also activated the purified receptor in the absence of an orthosteric agonist. In addition, it was found that purified mGlu5 was capable of activating the G protein Gs either upon stimulation with VU0424465 or glutamate, although the later induced a much weaker response. Our findings provide important mechanistic insights into mGlu5 G protein-dependent activity and selectivity.

Bacterial porins are water-filled β-barrel channels that allow translocation of solutes across the outer membrane. They feature a constriction zone, contributed by the plunging of extracellular loop 3 (L3) into the channel lumen. Porins are generally in the open state, but undergo gating in response to external voltages. To date the underlying mechanism is unclear. Here we report results from molecular dynamics simulations on the two porins of Providenica stuartii, Omp-Pst1 and Omp-Pst2, which display distinct voltage sensitivities. Voltage gating was observed in Omp-Pst2, where the binding of cations in-between L3 and the barrel wall results in exposing a conserved aromatic residue in the channel lumen, thereby halting ion permeation. Comparison of Omp-Pst1 and Omp-Pst2 structures and trajectories suggests that their sensitivity to voltage is encoded in the hydrogen-bonding network anchoring L3 onto the barrel wall, as we observed that it is the strength of this network that governs the probability of cations binding behind L3. That Omp-Pst2 gating is observed only when ions flow against the electrostatic potential gradient of the channel furthermore suggests a possible role for this porin in the regulation of charge distribution across the outer membrane and bacterial homeostasis.

Polycystin-2 (PC2) is a member of the TRPP subfamily of TRP channels and is present in ciliary membranes of the kidney. PC2 can be either homo-tetrameric, or heterotetrameric with PC1. PC2 shares a common transmembrane fold with other TRP channels, in addition to having a novel extracellular domain. Several TRP channels have been suggested to be regulated by lipids, including phosphatidylinositol phosphates (PIPs). We have combined molecular dynamics simulations with cryoelectron microscopy to explore possible lipid interactions sites on PC2. We propose that PC2 has a PIP-binding site close to the equivalent vanilloid/lipid-binding site in the TRPV1 channel. A 3.0 Å cryoelectron microscopy map reveals a binding site for cholesterol on PC2. Cholesterol interactions with the channel at this site are further characterized by MD simulations. These results help to position PC2 within an emerging model of the complex roles of lipids in the regulation and organization of ciliary membranes.