TSPO translocator proteins bind steroids and porphyrins, and they are implicated in many human diseases, for which they serve as biomarkers and therapeutic targets. TSPOs have tryptophan-rich sequences that are fhighly conserved from bacteria to mammals. We report crystal structures for Bacillus cereus TSPO (BcTSPO) down to 1.7Å resolution, including a complex with the benzodiazepine-like inhibitor PK11195. We also describe BcTSPO-mediated protoporphyrin IX (PpIX) reactions, including catalytic degradation to a previously undescribed heme derivative. We used structure-inspired mutations to investigate reaction mechanisms, and we showed that TSPOs from Xenopus and man have similar PpIX-directed activities. Although TSPOs have been regarded as transporters, the catalytic activity in PpIX degradation suggests physiological importance for TSPOs in protection against oxidative stress.

Mutations in the gene BEST1 are causally associated with as many as five clinically distinct retinal degenerative diseases, which are collectively referred to as the “bestrophinopathies”. These five associated diseases are: Best vitelliform macular dystrophy, autosomal recessive bestrophinopathy, adult-onset vitelliform macular dystrophy, autosomal dominant vitreoretinochoroidopathy, and retinitis pigmentosa. The most common of these is Best vitelliform macular dystrophy. Bestrophin 1 (Best1), the protein encoded by the gene BEST1, has been the subject of a great deal of research since it was first identified nearly two decades ago. Today we know that Best1 functions as both a pentameric anion channel and a regulator of intracellular Ca2+ signaling. Best1 is an integral membrane protein which, within the eye, is uniquely expressed in the retinal pigment epithelium where it predominantly localizes to the basolateral plasma membrane. Within the brain, Best1 expression has been documented in both glial cells and astrocytes where it functions in both tonic GABA release and glutamate transport. The crystal structure of Best1 has revealed critical information about how Best1 functions as an ion channel and how Ca2+ regulates that function. Studies using animal models have led to critical insights into the physiological roles of Best1 and advances in stem cell technology have allowed for the development of patient-derived, “disease in a dish” models. In this article we review our knowledge of Best1 and discuss prospects for near-term clinical trials to test therapies for the bestrophinopathies, a currently incurable and untreatable set of diseases.

Summary Inflammasomes are important sentinels of innate immune defense, sensing pathogens and inducing cell death in infected cells 1 . There are several inflammasome sensors that each detect and respond to specific pathogen- and damage-associated molecular patterns (PAMPs and DAMPs) 1 . In contrast to this one PAMP/DAMP to one sensor specificity, during infection, live pathogens can induce the release of multiple PAMPs and DAMPs, which could contemporaneously engage multiple inflammasome sensors 2 – 5 . Here we discovered that AIM2 regulated the innate immune sensors Pyrin and ZBP1 to drive inflammatory signaling and inflammatory cell death, PANoptosis, and provide host protection during infections with herpes simplex virus 1 (HSV1) and Francisella novicida . We also observed that AIM2, Pyrin and ZBP1 were members of a large multi-protein complex along with ASC, caspase-1, caspase-8, RIPK3, RIPK1 and FADD that drove inflammatory cell death. Collectively, our findings define a previously unknown regulatory connection and molecular interaction among AIM2, Pyrin and ZBP1 that drives assembly of an AIM2-mediated multi-protein complex that involves multiple inflammasome sensors and cell death regulators. These results represent a new paradigm in understanding the functions of these molecules in innate immunity and inflammatory cell death, suggesting new therapeutic targets for AIM2-, ZBP1- and Pyrin-mediated diseases.

Human bestrophin 1 (hBest1) is a calcium-activated chloride channel from the retinal pigment epithelium, where it can suffer mutations associated with vitelliform macular degeneration, or Best disease. We describe the structure of a bacterial homolog (KpBest) of hBest1 and functional characterizations of both channels. KpBest is a pentamer that forms a five-helix transmembrane pore, closed by three rings of conserved hydrophobic residues, and has a cytoplasmic cavern with a restricted exit. From electrophysiological analysis of structure-inspired mutations in KpBest and hBest1, we find a subtle control of ion selectivity in the bestrophins, including reversal of anion/cation selectivity, and dramatic activation by mutations at the exit restriction. A homology model of hBest1 shows the locations of disease-causing mutations and suggests possible roles in regulation.

Glucose monomycolate–loaded CD1b tetramers identify a subset of CD4+ T cells in patients with Mycobacterium tuberculosis infection.

Highlights d MLKL N-terminal executioner domain (NED) is auto-inhibited by the linker-brace d Inositol pentakisphosphate 2-kinase (IPPK) synthesizes IP 6 to regulate necroptosis d Selective inositol phosphate (IP) repertoire binds three distinct sites in NED d Hierarchical direct activation of MLKL is induced by three IPs (IP 6 >IP 4 RIP 5

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Human CD1a mediates foreign antigen recognition by a T cell clone, but the nature of possible T cell receptor interactions with CD1a-lipid are unknown. After incubating CD1a with a mycobacterial lipopeptide antigen, dideoxymycobactin (DDM), we identified and measured binding to a recombinant TCR (TRAV3/ TRBV3-1, KD ≈ 100µM). Detection of ternary CD1a-lipid-TCR interactions enabled development of CD1a tetramers and CD1a multimers with carbohydrate backbones (dextramers), which specifically stained T cells using a mechanism that was dependent on the precise stereochemistry of the peptide backbone and was blocked with a soluble TCR. Further, sorting of human T cells from unrelated tuberculosis patients for bright DDM-dextramer staining allowed recovery of T cells that were activated by CD1a and DDM. These studies demonstrate that the mechanism of T cell activation by lipopeptides occurs via ternary interactions of CD1a-antigen-TCR. Further, these studies demonstrate the existence of lipopeptide specific T cells in humans ex vivo.