SummaryP2X receptors are cation selective ion channels gated by extracellular ATP and implicated in diverse physiological processes, from synaptic transmission to inflammation to the sensing of taste and pain. Because P2X receptors are not related to other ion channel proteins of known structure, there is presently no molecular foundation for mechanisms of ligand-gating, allosteric modulation and ion permeation. Here we present crystal structures of the zebrafish P2X4 receptor in its closed, resting state. The chalice-shaped, trimeric receptor is knit together by subunit-subunit contacts implicated in ion channel gating and receptor assembly. Extracellular domains, rich in β-strands, have large acidic patches that may attract cations, through fenestrations, to vestibules near the ion channel. Within the transmembrane pore, the ‘gate’ is defined by an ~8 Ǻ slab of protein. We define the location of three non-canonical, intersubunit ATP binding sites and suggest that ATP binding promotes subunit rearrangement and ion channel opening.

The striatum integrates excitatory inputs from the cortex and the thalamus to control diverse functions. Although the striatum is thought to consist of sensorimotor, associative and limbic domains, their precise demarcations and whether additional functional subdivisions exist remain unclear. How striatal inputs are differentially segregated into each domain is also poorly understood. This study presents a comprehensive map of the excitatory inputs to the mouse striatum. The input patterns reveal boundaries between the known striatal domains. The most posterior striatum likely represents the 4th functional subdivision, and the dorsomedial striatum integrates highly heterogeneous, multimodal inputs. The complete thalamo-cortico-striatal loop is also presented, which reveals that the thalamic subregions innervated by the basal ganglia preferentially interconnect with motor-related cortical areas. Optogenetic experiments show the subregion-specific heterogeneity in the synaptic properties of striatal inputs from both the cortex and the thalamus. This projectome will guide functional studies investigating diverse striatal functions.DOI: http://dx.doi.org/10.7554/eLife.19103.001

Carboxyl-terminal binding protein (CtBP) is a transcriptional corepressor originally identified through its ability to interact with adenovirus E1A. The finding that CtBP-E1A interactions were regulated by the nicotinamide adeninine dinucleotides NAD ؉ and NADH raised the possibility that CtBP could serve as a nuclear redox sensor. This model requires differential binding affinities of NAD ؉ and NADH, which has been controversial. The structure of CtBP determined by x-ray diffraction revealed a tryptophan residue adjacent to the proposed nicotinamide adenine dinucleotide binding site. We find that this tryptophan residue shows strong fluorescence resonance energy transfer to bound NADH. In this report, we take advantage of these findings to measure the dissociation constants for CtBP with NADH and NAD ؉ . The affinity of NADH was determined by using fluorescence resonance energy transfer. The binding of NADH to protein is associated with an enhanced intensity of NADH fluorescence and a blue shift in its maximum. NAD ؉ affinity was estimated by measuring the loss of the fluorescence blue shift as NADH dissociates on addition of NAD ؉ . Our studies show a >100-fold higher affinity of NADH than NAD ؉ , consistent with the proposed function of CtBP as a nuclear redox sensor. Moreover, the concentrations of NADH and NAD ؉ required for half-maximal binding are approximately the same as their concentrations in the nuclear compartment. These findings support the possibility that changes in nuclear nicotinamide adenine dinucleotides could regulate the functions of CtBP in cell differentiation, development, or transformation.A n emerging theme in gene regulation is the dependence of transcriptional coregulators on molecules linked to cellular respiration. Acetyl-CoA is required by the histone acetyltransferase coactivators (1) and is perhaps the most central of all intermediary metabolites, bridging the major catabolic and anabolic processes to the Kreb's cycle, where its two carbons are converted to the respiratory product, CO 2 . ATP is important for essentially all cellular processes requiring energy, including the chromatin remodeling proteins involved in modifying nucleosomal structure (2). The pervasive involvement of acetyl-CoA and ATP in cellular processes generally obscures recognition of their specific contributions to transcriptional regulation, however. In addition, the relatively small changes in acetyl-CoA and ATP that occur during metabolism may not be suitable for regulating the activities of the relevant enzymes.The breakdown of carbon sources is also associated with the reduction of the nicotinamide adenine dinucleotide NAD ϩ to NADH. NADH serves as an electron carrier that transports reducing equivalents to the electron transport chain, where ATP is synthesized. The synthesis of ATP involves oxidative phosphorylation, wherein NADH is oxidized to NAD ϩ and molecular oxygen is reduced to water. These roles of NAD ϩ and NADH provide additional, albeit somewhat indirect, connections between energy homeostas...