Adenosine triphosphate (ATP), the chemical energy currency of biology, is synthesized in eukaryotic cells primarily by the mitochondrial ATP synthase. ATP synthases operate by a rotary catalytic mechanism where proton translocation through the membrane-inserted FO region is coupled to ATP synthesis in the catalytic F1 region via rotation of a central rotor subcomplex. We report here single particle electron cryomicroscopy (cryo-EM) analysis of the bovine mitochondrial ATP synthase. Combining cryo-EM data with bioinformatic analysis allowed us to determine the fold of the a subunit, suggesting a proton translocation path through the FO region that involves both the a and b subunits. 3D classification of images revealed seven distinct states of the enzyme that show different modes of bending and twisting in the intact ATP synthase. Rotational fluctuations of the c8-ring within the FO region support a Brownian ratchet mechanism for proton-translocation-driven rotation in ATP synthases.DOI: http://dx.doi.org/10.7554/eLife.10180.001

T cells represent a critical effector of cell-mediated immunity. Activated T cells engage in metabolic reprogramming during effector differentiation to accommodate dynamic changes in energy demands. Here, we show that the hormone, insulin, and downstream signaling through its insulin receptor shape adaptive immune function through modulating T cell metabolism. T cells lacking insulin receptor expression (LckCre+ Insr) show reduced antigen-specific proliferation and compromised production of pro-inflammatory cytokines. In vivo, T cell-specific insulin receptor deficiency reduces T cell-driven colonic inflammation. In a model of severe influenza infection with A/PR8 (H1N1), lack of insulin receptor on T cells curtails antigen-specific immunity to influenza viral antigens. Mechanistically, insulin receptor signaling reinforces a metabolic program that supports T cell nutrient uptake and associated glycolytic and respiratory capacities. These data highlight insulin receptor signaling as an important node integrating immunometabolic pathways to drive optimal T cell effector function in health and disease.

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxic activity of many environmental xenobiotics. However, its role in innate immune responses during viral infection is not fully understood. Here we demonstrate that constitutive AHR signaling negatively regulates the type I interferon (IFN-I) response during infection with various types of virus. Virus-induced IFN-β production was enhanced in AHR- IFN-I-mediated innate response and, further, suggests that the AHR-TIPARP axis is a potential therapeutic target for enhancing antiviral responses.AHR was originally discovered as a xenobiotic sensor that mediates the toxicity of the persistent environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), more commonly known as dioxin [1][2][3][4] . Activation of AHR induces its target genes, including those encoding cytochrome P4501A1, cytochrome P4501B1, AHR repressor, TCDD-inducible poly(ADP-ribose)polymerase (TIPARP) and aldehyde dehydrogenase 1A3 (refs. 1,2,5-9), which are involved in the adaptive metabolism of xenobiotic compounds. This property of AHR has been implicated in host defense against bacterial infection, as certain bacterial pigmented virulence factors are AHR agonists that are subsequently metabolized by AHR-regulated drug-metabolizing enzymes 10 . Studies of AHR-deficient mice have identified important physiological roles for AHR in response to endogenous ligands in cell cycle regulation, cell differentiation and immune responses 8,[11][12][13][14] . In relation to this, several putative endogenous ligands for the AHR have also been reported, including heme metabolites, arachidonic acids or leukotrienes and tryptophan metabolites, such as 6-formylindolo(3,2-b)carbazole (FICZ) and kynurenine (Kyn) 2,8,15 .There has been increased interest in understanding the role of AHR in immunity.Several reports, most of which are based mainly on experiments with dioxin treatment, have shown that the AHR is involved in the differentiation and/or function of T cells, macrophages and dendritic cells 7,9,11,[16][17][18][19][20][21] . AHR has been implicated in the control of acute graft-versus-host disease and autoimmunity 11,12,21 . Dioxin-activated AHR also reduces the survival rate of mice infected with influenza A virus 22,23 and indirectly suppresses the proliferation and differentiation of virus-specific CD8 + T cells via its regulatory role in dendritic cells 24 . FICZ and dioxin diminish CD8 + T cell responsiveness, whereas dioxin, but not FICZ, affects neutrophil recruitment or pulmonary inducible nitric oxide synthase (iNOS) induction in response to influenza virus infection 25 .Tryptophan metabolites such as Kyn are upregulated during inflammation and/or tumor progression in several types of immune and tumor cells through the catalytic activity of tryptophan dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO), which catalyze the first step in the formation of Kyn from tryptophan 2,9 . This increase in Kyn leads to an increase in regulatory T c...