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8 Janelia Publications

Showing 1-8 of 8 results
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    11/17/17 | Structural basis of bacterial transcription activation.
    Liu B, Hong C, Huang RK, Yu Z, Steitz TA
    Science (New York, N.Y.). 2017 Nov 17;358(6365):947-951. doi: 10.1126/science.aao1923

    In bacteria, the activation of gene transcription at many promoters is simple and only involves a single activator. The cyclic adenosine 3',5'-monophosphate receptor protein (CAP), a classic activator, is able to activate transcription independently through two different mechanisms. Understanding the class I mechanism requires an intact transcription activation complex (TAC) structure at a high resolution. Here we report a high-resolution cryo-electron microscopy structure of an intact Escherichia coli class I TAC containing a CAP dimer, a σ(70)-RNA polymerase (RNAP) holoenzyme, a complete class I CAP-dependent promoter DNA, and a de novo synthesized RNA oligonucleotide. The structure shows how CAP wraps the upstream DNA and how the interactions recruit RNAP. Our study provides a structural basis for understanding how activators activate transcription through the class I recruitment mechanism.

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    08/07/17 | Near-atomic resolution cryoelectron microscopy structure of the 30-fold homooligomeric SpoIIIAG channel essential to spore formation in Bacillus subtilis.
    Zeytuni N, Hong C, Flanagan KA, Worrall LJ, Theiltges KA, Vuckovic M, Huang RK, Massoni SC, Camp AH, Yu Z, Strynadka NC
    Proceedings of the National Academy of Sciences of the United States of America. 2017 Aug 07:. doi: 10.1073/pnas.1704310114

    Bacterial sporulation allows starving cells to differentiate into metabolically dormant spores that can survive extreme conditions. Following asymmetric division, the mother cell engulfs the forespore, surrounding it with two bilayer membranes. During the engulfment process, an essential channel, the so-called feeding tube apparatus, is thought to cross both membranes to create a direct conduit between the mother cell and the forespore. At least nine proteins are required to create this channel, including SpoIIQ and SpoIIIAA-AH. Here, we present the near-atomic resolution structure of one of these proteins, SpoIIIAG, determined by single-particle cryo-EM. A 3D reconstruction revealed that SpoIIIAG assembles into a large and stable 30-fold symmetric complex with a unique mushroom-like architecture. The complex is collectively composed of three distinctive circular structures: a 60-stranded vertical β-barrel that forms a large inner channel encircled by two concentric rings, one β-mediated and the other formed by repeats of a ring-building motif (RBM) common to the architecture of various dual membrane secretion systems of distinct function. Our near-atomic resolution structure clearly shows that SpoIIIAG exhibits a unique and dramatic adaptation of the RBM fold with a unique β-triangle insertion that assembles into the prominent channel, the dimensions of which suggest the potential passage of large macromolecules between the mother cell and forespore during the feeding process. Indeed, mutation of residues located at key interfaces between monomers of this RBM resulted in severe defects both in vivo and in vitro, providing additional support for this unprecedented structure.

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    08/04/17 | Best practices for managing large CryoEM facilities.
    Alewijnse B, Ashton AW, Chambers MG, Chen S, Cheng A, Ebrahim M, Eng ET, Hagen WJ, Koster AJ, Lopez CS, Lukoyanova N, Ortega J, Renault L, Reyntjens S, Rice WJ, Scapin G, Schrijver R, Siebert A, Stagg SM, et al
    Journal of Structural Biology. 2017-08-04:. doi: 10.1016/j.jsb.2017.07.011

    This paper provides an overview of the discussion and presentations from the Workshop on the Management of Large CryoEM Facilities held at the New York Structural Biology Center, New York, NY on February 6–7, 2017. A major objective of the workshop was to discuss best practices for managing cryoEM facilities. The discussions were largely focused on supporting single-particle methods for cryoEM and topics included: user access, assessing projects, workflow, sample handling, microscopy, data management and processing, and user training.

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    04/06/17 | Diverse protocols for correlative super-resolution fluorescence imaging and electron microscopy of chemically fixed samples.
    Kopek BG, Paez-Segala MG, Shtengel G, Sochacki KA, Sun MG, Wang Y, Xu CS, Van Engelenburg SB, Taraska JW, Looger LL, Hess HF
    Nature Protocols. 2017 May;12(5):916-946. doi: 10.1038/nprot.2017.017

    Our groups have recently developed related approaches for sample preparation for super-resolution imaging within endogenous cellular environments using correlative light and electron microscopy (CLEM). Four distinct techniques for preparing and acquiring super-resolution CLEM data sets for aldehyde-fixed specimens are provided, including Tokuyasu cryosectioning, whole-cell mount, cell unroofing and platinum replication, and resin embedding and sectioning. The choice of the best protocol for a given application depends on a number of criteria that are discussed in detail. Tokuyasu cryosectioning is relatively rapid but is limited to small, delicate specimens. Whole-cell mount has the simplest sample preparation but is restricted to surface structures. Cell unroofing and platinum replication creates high-contrast, 3D images of the cytoplasmic surface of the plasma membrane but is more challenging than whole-cell mount. Resin embedding permits serial sectioning of large samples but is limited to osmium-resistant probes, and is technically difficult. Expected results from these protocols include super-resolution localization (∼10-50 nm) of fluorescent targets within the context of electron microscopy ultrastructure, which can help address cell biological questions. These protocols can be completed in 2-7 d, are compatible with a number of super-resolution imaging protocols, and are broadly applicable across biology.

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    12/14/16 | Near-atomic-resolution cryo-EM analysis of the Salmonella T3S injectisome basal body.
    Worrall LJ, Hong C, Vuckovic M, Deng W, Bergeron JR, Majewski DD, Huang RK, Spreter T, Finlay BB, Yu Z, Strynadka NC
    Nature. 2016 Dec 14:. doi: 10.1038/nature20576

    The type III secretion (T3S) injectisome is a specialized protein nanomachine that is critical for the pathogenicity of many Gram-negative bacteria, including purveyors of plague, typhoid fever, whooping cough, sexually transmitted infections and major nosocomial infections. This syringe-shaped 3.5-MDa macromolecular assembly spans both bacterial membranes and that of the infected host cell. The internal channel formed by the injectisome allows for the direct delivery of partially unfolded virulence effectors into the host cytoplasm. The structural foundation of the injectisome is the basal body, a molecular lock-nut structure composed predominantly of three proteins that form highly oligomerized concentric rings spanning the inner and outer membranes. Here we present the structure of the prototypical Salmonella enterica serovar Typhimurium pathogenicity island 1 basal body, determined using single-particle cryo-electron microscopy, with the inner-membrane-ring and outer-membrane-ring oligomers defined at 4.3 Å and 3.6 Å resolution, respectively. This work presents the first, to our knowledge, high-resolution structural characterization of the major components of the basal body in the assembled state, including that of the widespread class of outer-membrane portals known as secretins.

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    11/16/16 | A near-atomic structure of the dark apoptosome provides insight into assembly and activation.
    Cheng TC, Akey IV, Yuan S, Yu Z, Ludtke SJ, Akey CW
    Structure (London, England : 1993). 2016 Nov 16;25(1):40-52. doi: 10.1016/j.str.2016.11.002

    In Drosophila, the Apaf-1-related killer (Dark) forms an apoptosome that activates procaspases. To investigate function, we have determined a near-atomic structure of Dark double rings using cryo-electron microscopy. We then built a nearly complete model of the apoptosome that includes 7- and 8-blade β-propellers. We find that the preference for dATP during Dark assembly may be governed by Ser325, which is in close proximity to the 2' carbon of the deoxyribose ring. Interestingly, β-propellers in V-shaped domains of the Dark apoptosome are more widely separated, relative to these features in the Apaf-1 apoptosome. This wider spacing may be responsible for the lack of cytochrome c binding to β-propellers in the Dark apoptosome. Our structure also highlights the roles of two loss-of-function mutations that may block Dark assembly. Finally, the improved model provides a framework to understand apical procaspase activation in the intrinsic cell death pathway.

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    10/04/16 | A near atomic structure of the active human apoptosome.
    Cheng TC, Hong C, Akey IV, Yuan S, Akey CW
    eLife. 2016 Oct 04;5:e17755. doi: 10.7554/eLife.17755

    In response to cell death signals, an active apoptosome is assembled from Apaf-1 and procaspase-9 (pc-9). Here we report a near atomic structure of the active human apoptosome determined by cryo-electron microscopy. The resulting model gives insights into cytochrome c binding, nucleotide exchange and conformational changes that drive assembly. During activation an acentric disk is formed on the central hub of the apoptosome. This disk contains four Apaf-1/pc-9 CARD pairs arranged in a shallow spiral with the fourth pc-9 CARD at lower occupancy. On average, Apaf-1 CARDs recruit 3 to 5 pc-9 molecules to the apoptosome and one catalytic domain may be parked on the hub, when an odd number of zymogens are bound. This suggests a stoichiometry of one or at most, two pc-9 dimers per active apoptosome. Thus, our structure provides a molecular framework to understand the role of the apoptosome in programmed cell death and disease.

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    08/01/13 | Electron cryotomography of ESCRT assemblies and dividing Sulfolobus cells suggests that spiraling filaments are involved in membrane scission.
    Dobro MJ, Samson RY, Yu Z, McCullough J, Ding HJ, Chong PL, Bell SD, Jensen GJ
    Molecular Biology of the Cell. 2013 Aug;24(15):2319-27. doi: 10.1091/mbc.E12-11-0785

    The endosomal-sorting complex required for transport (ESCRT) is evolutionarily conserved from Archaea to eukaryotes. The complex drives membrane scission events in a range of processes, including cytokinesis in Metazoa and some Archaea. CdvA is the protein in Archaea that recruits ESCRT-III to the membrane. Using electron cryotomography (ECT), we find that CdvA polymerizes into helical filaments wrapped around liposomes. ESCRT-III proteins are responsible for the cinching of membranes and have been shown to assemble into helical tubes in vitro, but here we show that they also can form nested tubes and nested cones, which reveal surprisingly numerous and versatile contacts. To observe the ESCRT-CdvA complex in a physiological context, we used ECT to image the archaeon Sulfolobus acidocaldarius and observed a distinct protein belt at the leading edge of constriction furrows in dividing cells. The known dimensions of ESCRT-III proteins constrain their possible orientations within each of these structures and point to the involvement of spiraling filaments in membrane scission.

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