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5 Janelia Publications

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    10/12/22 | Structure of the OMEGA nickase IsrB in complex with ωRNA and target DNA.
    Hirano S, Kappel K, Altae-Tran H, Faure G, Wilkinson ME, Kannan S, Demircioglu FE, Yan R, Shiozaki M, Yu Z, Makarova KS, Koonin EV, Macrae RK, Zhang F
    Nature. 2022 Oct 12;610(7932):575-581. doi: 10.1038/s41586-022-05324-6

    RNA-guided systems, such as CRISPR-Cas, combine programmable substrate recognition with enzymatic function, a combination that has been used advantageously to develop powerful molecular technologies. Structural studies of these systems have illuminated how the RNA and protein jointly recognize and cleave their substrates, guiding rational engineering for further technology development. Recent work identified a new class of RNA-guided systems, termed OMEGA, which include IscB, the likely ancestor of Cas9, and the nickase IsrB, a homologue of IscB lacking the HNH nuclease domain. IsrB consists of only around 350 amino acids, but its small size is counterbalanced by a relatively large RNA guide (roughly 300-nt ωRNA). Here, we report the cryogenic-electron microscopy structure of Desulfovirgula thermocuniculi IsrB (DtIsrB) in complex with its cognate ωRNA and a target DNA. We find the overall structure of the IsrB protein shares a common scaffold with Cas9. In contrast to Cas9, however, which uses a recognition (REC) lobe to facilitate target selection, IsrB relies on its ωRNA, part of which forms an intricate ternary structure positioned analogously to REC. Structural analyses of IsrB and its ωRNA as well as comparisons to other RNA-guided systems highlight the functional interplay between protein and RNA, advancing our understanding of the biology and evolution of these diverse systems.

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    09/03/22 | The SARS-CoV-2 accessory protein Orf3a is not an ion channel, but does interact with trafficking proteins
    Alexandria N. Miller , Patrick R. Houlihan , Ella Matamala , Deny Cabezas-Bratesco , Gi Young Lee , Ben Cristofori-Armstrong , Tanya L. Dilan , Silvia Sanchez-Martinez , Doreen Matthies , Rui Yan , Zhiheng Yu , Dejian Ren , Sebastian E. Brauchi , David E. Clapham
    bioRxiv. 2022 Sep 03:. doi: 10.1101/2022.09.02.506428

    The severe acute respiratory syndrome associated coronavirus 2 (SARS-CoV-2) and SARS-CoV-1 accessory protein Orf3a colocalizes with markers of the plasma membrane, endocytic pathway, and Golgi apparatus. Some reports have led to annotation of both Orf3a proteins as a viroporin. Here we show that neither SARS-CoV-2 nor SARS-CoV-1 form functional ion conducting pores and that the conductances measured are common contaminants in overexpression and with high levels of protein in reconstitution studies. Cryo-EM structures of both SARS-CoV-2 and SARS-CoV-1 Orf3a display a narrow constriction and the presence of a basic aqueous vestibule, which would not favor cation permeation. We observe enrichment of the late endosomal marker Rab7 upon SARS-CoV-2 Orf3a overexpression, and co-immunoprecipitation with VPS39. Interestingly, SARS-CoV-1 Orf3a does not cause the same cellular phenotype as SARS-CoV-2 Orf3a and does not interact with VPS39. To explain this difference, we find that a divergent, unstructured loop of SARS-CoV-2 Orf3a facilitates its binding with VPS39, a HOPS complex tethering protein involved in late endosome and autophagosome fusion with lysosomes. We suggest that the added loop enhances SARS-CoV-2 Orf3a ability to co-opt host cellular trafficking mechanisms for viral exit or host immune evasion.

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    08/12/22 | Isolation, cryo-laser scanning confocal microscope imaging and cryo-FIB milling of mouse glutamatergic synaptosomes.
    Gogoi P, Shiozaki M, Gouaux E
    PLoS One. 2022 Aug 12;17(8):e0271799. doi: 10.1371/journal.pone.0271799

    Ionotropic glutamate receptors (iGluRs) at postsynaptic terminals mediate the majority of fast excitatory neurotransmission in response to release of glutamate from the presynaptic terminal. Obtaining structural information on the molecular organization of iGluRs in their native environment, along with other signaling and scaffolding proteins in the postsynaptic density (PSD), and associated proteins on the presynaptic terminal, would enhance understanding of the molecular basis for excitatory synaptic transmission in normal and in disease states. Cryo-electron tomography (ET) studies of synaptosomes is one attractive vehicle by which to study iGluR-containing excitatory synapses. Here we describe a workflow for the preparation of glutamatergic synaptosomes for cryo-ET studies. We describe the utilization of fluorescent markers for the facile detection of the pre and postsynaptic terminals of glutamatergic synaptosomes using cryo-laser scanning confocal microscope (cryo-LSM). We further provide the details for preparation of lamellae, between ~100 to 200 nm thick, of glutamatergic synaptosomes using cryo-focused ion-beam (FIB) milling. We monitor the lamella preparation using a scanning electron microscope (SEM) and following lamella production, we identify regions for subsequent cryo-ET studies by confocal fluorescent imaging, exploiting the pre and postsynaptic fluorophores.

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    06/02/22 | Allosteric interactions prime androgen receptor dimerization and activation.
    Wasmuth EV, Broeck AV, LaClair JR, Hoover EA, Lawrence KE, Paknejad N, Pappas K, Matthies D, Wang B, Feng W, Watson PA, Zinder JC, Karthaus WR, de la Cruz MJ, Hite RK, Manova-Todorova K, Yu Z, Weintraub ST, Klinge S, Sawyers CL
    Molecular Cell. 2022 Jun 02;82(11):2021-31. doi: 10.1016/j.molcel.2022.03.035

    The androgen receptor (AR) is a nuclear receptor that governs gene expression programs required for prostate development and male phenotype maintenance. Advanced prostate cancers display AR hyperactivation and transcriptome expansion, in part, through AR amplification and interaction with oncoprotein cofactors. Despite its biological importance, how AR domains and cofactors cooperate to bind DNA has remained elusive. Using single-particle cryo-electron microscopy, we isolated three conformations of AR bound to DNA, showing that AR forms a non-obligate dimer, with the buried dimer interface utilized by ancestral steroid receptors repurposed to facilitate cooperative DNA binding. We identify novel allosteric surfaces which are compromised in androgen insensitivity syndrome and reinforced by AR's oncoprotein cofactor, ERG, and by DNA-binding motifs. Finally, we present evidence that this plastic dimer interface may have been adopted for transactivation at the expense of DNA binding. Our work highlights how fine-tuning AR's cooperative interactions translate to consequences in development and disease.

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    05/16/22 | In situ cryo-electron tomography reveals the asymmetric architecture of mammalian sperm axonemes
    Zhen Chen , Garrett A. Greenan , Momoko Shiozaki , Yanxin Liu , Will M. Skinner , Xiaowei Zhao , Shumei Zhao , Rui Yan , Caiying Guo , Zhiheng Yu , Polina V. Lishko , David A. Agard , Ronald D. Vale
    bioRxiv. 2022 May 16:. doi: 10.1101/2022.05.15.492011

    The flagella of mammalian sperm display non-planar, asymmetric beating, in contrast to the planar, symmetric beating of flagella from sea urchin sperm and unicellular organisms. The molecular basis of this difference is unclear. Here, we perform in situ cryo-electron tomography of mouse and human sperm axonemes, providing the highest resolution structural information to date. Our subtomogram averages reveal mammalian sperm- specific protein complexes within the outer microtubule doublets, the radial spokes and nexin-dynein regulatory complexes. The locations and structures of these complexes suggest potential roles in enhancing the mechanical strength of mammalian sperm axonemes and regulating dynein-based axonemal bending. Intriguingly, we find that each of the nine outer microtubule doublets is decorated with a distinct combination of sperm- specific complexes. We propose that this asymmetric distribution of proteins differentially regulates the sliding of each microtubule doublet and may underlie the asymmetric beating of mammalian sperm.

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