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Abstract Burkholderia cenocepacia is an opportunistic and infective bacterium containing an orphan DNA methyltransferase called M.BceJIV with roles in regulating gene expression and motility of the bacterium. M.BceJIV recognizes a GTWWAC motif (where W can be an adenine or a thymine) and methylates N6 of the adenine at the fifth base position. Here, we present crystal structures of M.BceJIV/DNA/sinefungin ternary complex and allied biochemical, computational, and thermodynamic analyses. Remarkably, the structures show not one, but two DNA substrates bound to the M.BceJIV dimer, with each monomer contributing to the recognition of two recognition sequences. We also show that methylation at the two recognition sequences occurs independently, and that the GTWWAC motifs are enriched in intergenic regions in the genomes of B. cenocepacia strains. We further computationally assess the interactions underlying the affinities of different ligands (SAM, SAH, and sinefungin) for M.BceJIV, as a step towards developing selective inhibitors for limiting B. cenocepacia infection.

Abstract The metabotropic glutamate receptors (mGluRs) are neuromodulatory family C G protein coupled receptors which assemble as dimers and allosterically couple extracellular ligand binding domains (LBDs) to transmembrane domains (TMDs) to drive intracellular signaling. Pharmacologically, mGluRs can be targeted at the LBDs by glutamate and synthetic orthosteric compounds or at the TMDs by allosteric modulators. Despite the potential of allosteric compounds as therapeutics, an understanding of the functional and structural basis of their effects is limited. Here we use multiple approaches to dissect the functional and structural effects of orthosteric versus allosteric ligands. We find, using electrophysiological and live cell imaging assays, that both agonists and positive allosteric modulators (PAMs) can drive activation and internalization of group II and III mGluRs. The effects of PAMs are pleiotropic, boosting the maximal response to orthosteric agonists and serving independently as internalization-biased agonists across mGluR subtypes. Motivated by this and intersubunit FRET analyses, we determine cryo-electron microscopy structures of mGluR3 in the presence of either an agonist or antagonist alone or in combination with a PAM. These structures reveal PAM-driven re-shaping of intra- and inter-subunit conformations and provide evidence for a rolling TMD dimer interface activation pathway that controls G protein and beta-arrestin coupling.

Summary: G proteins are major signaling partners for G protein-coupled receptors (GPCRs). Although stepwise structural changes during GPCR–G protein complex formation and guanosine diphosphate (GDP) release have been reported, no information is available with regard to guanosine triphosphate (GTP) binding. Here, we used a novel Bayesian integrative modeling framework that combines data from hydrogen-deuterium exchange mass spectrometry, tryptophan-induced fluorescence quenching, and metadynamics simulations to derive a kinetic model and atomic-level characterization of stepwise conformational changes incurred by the β2-adrenergic receptor (β2AR)-Gs complex after GDP release and GTP binding. Our data suggest rapid GTP binding and GTP-induced dissociation of Gαs from β2AR and Gβγ, as opposed to a slow closing of the Gαs α-helical domain (AHD). Yeast-two-hybrid screening using Gαs AHD as bait identified melanoma-associated antigen D2 (MAGE D2) as a novel AHD-binding protein, which was also shown to accelerate the GTP-induced closing of the Gαs AHD.

G Protein-Coupled Receptors (GPCRs) are a large family of membrane proteins with pluridimensional signaling profiles. They undergo ligand-specific conformational changes, which in turn lead to the differential activation of intracellular signaling proteins and the consequent triggering of a variety of biological responses. This conformational plasticity directly impacts our understanding of GPCR signaling and therapeutic implications, as do ligand-specific kinetic differences in GPCR-induced transducer activation/coupling or GPCR-transducer complex stability. High-resolution experimental structures of ligand-bound GPCRs in the presence or absence of interacting transducers provide important, yet limited, insights into the highly dynamic process of ligand-induced activation or inhibition of these receptors. We and others have complemented these studies with computational strategies aimed at characterizing increasingly accurate metastable conformations of GPCRs using a combination of metadynamics simulations, state-of-the-art algorithms for statistical analyses of simulation data, and artificial intelligence-based tools. This minireview provides an overview of these approaches as well as lessons learned from them towards the identification of conformational states that may be difficult or even impossible to characterize experimentally and yet important to discover new GPCR ligands.

The metabotropic glutamate receptors (mGluRs) form a family of neuromodulatory G-protein-coupled receptors that contain both a seven-helix transmembrane domain (TMD) and a large extracellular ligand-binding domain (LBD) which enables stable dimerization. Although numerous studies have revealed variability across subtypes in the initial activation steps at the level of LBD dimers, an understanding of inter-TMD interaction and rearrangement remains limited. Here, we use a combination of single molecule fluorescence, molecular dynamics, functional assays, and conformational sensors to reveal that distinct TMD assembly properties drive differences between mGluR subtypes. We uncover a variable region within transmembrane helix 4 (TM4) that contributes to homo- and heterodimerization in a subtype-specific manner and tunes orthosteric, allosteric, and basal activation. We also confirm a critical role for a conserved inter-TM6 interface in stabilizing the active state during orthosteric or allosteric activation. Together this study shows that inter-TMD assembly and dynamic rearrangement drive mGluR function with distinct properties between subtypes.

Objectives. To analyze War on Drugs encounters and their relationships to health care utilization among White people who use drugs (PWUD) in 22 Appalachian rural counties in Kentucky, West Virginia, Ohio, and North Carolina. Methods. We recruited White PWUD using chain referral sampling in 2018 to 2020. Surveys asked about criminal-legal encounters, unmet health care needs, and other covariates. We used generalized estimating equations to regress unmet need on criminal-legal encounters in multivariable models. Results. In this sample (n = 957), rates of stop and search, arrest, incarceration, and community supervision were high (44.0%, 26.8%, 36.3%, and 31.1%, respectively), as was unmet need (68.5%). Criminal-legal encounters were unrelated to unmet need (stops: adjusted prevalence ratio [APR] = 1.13; 95% confidence interval [CI] = 0.97, 1.32; arrest: APR = 0.95; 95% CI = 0.78, 1.15; incarceration: APR = 1.01; 95% CI = 0.89, 1.14; community supervision: APR = 0.99; 95% CI = 0.90, 1.09). Conclusions. Contrasting with findings from predominantly Black urban areas, criminal-legal encounters and unmet need were unrelated among White Appalachian PWUD. Research should explore whether and under what conditions White supremacy's benefits might buffer adverse impacts of the War on Drugs in Appalachia. ( Am J Public Health . 2024;114(10):1086-1096. https://doi.org/10.2105/AJPH.2024.307744).

Criminalizing young people, particularly Black- and Brown-identified young people, has increasingly been a feature of US rhetoric, policies, and practices. Thus, the domains in which young people are exposed to the legal system have continued to expand, encompassing their communities, schools, and homes. Importantly, public health researchers have begun exploring links between legal system exposure and health, although this literature is primarily focused at the interpersonal level and assesses associations within a single domain or in adulthood.Using critical race theory and ecosocial theory of disease distribution, we identified potential policy-level determinants of criminalization and briefly summarized the literature on downstream health outcomes among young people. Our analysis suggests that policy decisions may facilitate the targeting of structurally marginalized young people across domains.Future research should (1) position these legislative decisions as primary exposures of interest to understand their association with health among young people and inform institutional-level intervention, (2) measure the totality of exposure to the criminal legal system across domains, and (3) use theory to examine the complex ways racism operates institutionally to shape inequitable distributions of associated health outcomes.