IntasomeSalk researchers captured the structure of a protein complex called an intasome (center) that lets viruses similar to HIV establish permanent infection in their hosts. The intasome hijacks host genomic material, DNA (white) and histones (beige), and irreversibly inserts viral DNA (blue).” The image was created by Jamie Simon and Dmitry Lyumkis. Work that led to the 3D map was published in: Ballandras-Colas A, Brown M, Cook NJ, Dewdney TG, Demeler B, Cherepanov P, Lyumkis D, & Engelman AN. (2016). Cryo-EM reveals a novel octameric integrase structure for ?-retroviral intasome function. Nature, 530(7590), 358—361 CRISPRRNA incorporated into the CRISPR surveillance complex is positioned to scan across foreign DNA. Cryo-EM density from a 3Å reconstruction is shown as a yellow mesh. See: Chowdhury, S., J. Carter, M. F. Rollins, S. M. Golden, R. N. Jackson, C. Hoffmann, L. Nosaka, J. Bondy-Denomy, K. L. Maxwell, A. R. Davidson, E. R. Fischer, G. C. Lander, and B. Wiedenheft. 2017. Structure Reveals Mechanisms of Viral Suppressors that Intercept a CRISPR RNA-Guided Surveillance Complex. Cell 169:47-57 e11. CRISPRThis image shows how the CRISPR surveillance complex is disabled by two copies of anti-CRISPR protein AcrF1 (red) and one AcrF2 (light green). These anti-CRISPRs block access to the CRISPR RNA (green tube) preventing the surveillance complex from scanning and targeting invading viral DNA for destruction. See: Chowdhury, S., J. Carter, M. F. Rollins, S. M. Golden, R. N. Jackson, C. Hoffmann, L. Nosaka, J. Bondy-Denomy, K. L. Maxwell, A. R. Davidson, E. R. Fischer, G. C. Lander, and B. Wiedenheft. 2017. Structure Reveals Mechanisms of Viral Suppressors that Intercept a CRISPR RNA-Guided Surveillance Complex. Cell 169:47-57 e11. Human AdenovirusThe cryo-EM structure of human adenovirus D26 (HAdV-D26) at near atomic resolution (3.7 Å), determined in collaboration with the NRAMM facility*. In difference to archetype HAdV-C5, the HAdV-D26 is a low seroprevalent viral vector, which is being used to generate Ebola virus vaccines. See: Yu, X., D. Veesler, M. G. Campbell, M. E. Barry, F. J. Asturias, M. A. Barry, and V. S. Reddy. 2017. Cryo-EM structure of human adenovirus D26 reveals the conservation of structural organization among human adenoviruses. Sci Adv 3:e1602670. Addressing Preferred OrientationSingle-particle cryogenic electron microscopy (cryoEM) is a powerful technique to visualize the atomic structure of biological macromolecules. One common issue in cryoEM is that of preferred orientation - the problem that macromolecular particles show only limited views when imaged, preventing reconstruction of a high resolution structure. One way of overcoming this is through physical tilting of the stage, which as illustrated here by both the atomic model of hemagglutinin and a Campbell soup can. This introduces new views of the particle, making high resolution cryoEM reconstructions of preferred orientated samples possible. See: Tan, Y. Z., P. R. Baldwin, J. H. Davis, J. R. Williamson, C. S. Potter, B. Carragher, and D. Lyumkis. 2017. Addressing preferred specimen orientation in single-particle cryo-EM through tilting. Nature methods 14:793-796. Movies Enhance CryoEM ImagesA problem in cryoEM is the blurring in images due to beam-induced sample movement and stage instabilities. The article by Campbell et al. (pp. 1823–1828) describes a method based on movies recorded of ice-embedded samples during beam exposure to track the movement. The movies can be processed to reduce or eliminate blurring by aligning individual frames (symbolized by the film strip in the figure) to compensate for the sample movement (the resulting unblurred image is shown under the magnifying glass). The new method was tested using rotavirus particles (seen in the background), demonstrating increased resolution of the final reconstruction after unblurring.
Campbell MG, Cheng A, Brilot AF, Moeller A, Lyumkis D, Veesler D, Pan J, Harrison SC, Potter CS, Carragher B, Grigorieff N. (2012). Movies of ice-embedded particles enhance resolution in electron cryo-microscopy. Structure, 20, 1823-1828.