Instruct-ERIC CZ webinar recording
You can now play the recording of Instruct-ERIC webinar hosted by Czech Infrastructure for Integrative Structural Biology (CIISB) with presentations of Pavel Plevka, Jan Dohnálek, and Lukáš Trantírek.
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Structural changes in iflavirus particles that enable genome release of SBV, SBPV, and DWV. Native virions (A, F, and K), genome-containing particles at acidic pH (B, G, and L), open particles containing genomes (C, H, and M), open particles without genomes (D, I, and N), and empty capsids resulting from genome release (E, J, and O). Individual panels show cryo-EM reconstructions of particles rainbow colored on the basis of the distance of the particle surface from its center. (C), (H), and (N) show projection images of representative particles, since 3D reconstructions could not be calculated because of structural heterogeneity of the particles. Scale bar, 10 nm.
Significance
The family Iflaviridae includes economically important viruses of the western honeybee such as deformed wing virus, slow bee paralysis virus, and sacbrood virus. Iflaviruses have nonenveloped virions and capsids organized with icosahedral symmetry. The genome release of iflaviruses can be induced in vitro by exposure to acidic pH, implying that they enter cells by endocytosis. Genome release intermediates of iflaviruses have not been structurally characterized. Here, P. Plevka et.al. show that conformational changes and expansion of iflavirus RNA genomes, which are induced by acidic pH, trigger the opening of iflavirus particles. Capsids of slow bee paralysis virus and sacbrood virus crack into pieces. In contrast, capsids of deformed wing virus are more flexible and open like flowers to re- lease their genomes. The large openings in iflavirus particles enable the fast exit of genomes from capsids, which decreases the probability of genome degradation by the RNases present in endosomes.
Škubník, K., Sukeník, L. Buchta, D., Füzik, T., Procházková, M., Moravcová, J., Šmerdová, L., Přidal, A.,Vácha, R., and Plevka, P.: Capsid opening enables genome release of iflaviruses, Sci. Adv. 2021, 7, eabd7130, DOI: 10.1126/sciadv.abd7130
Three states of HelD color-coded according to the domain structure
Libor Krásný and Jan Dohnálek Research Groups
Significance
RNA synthesis is central to life, and RNA polymerase (RNAP) depends on accessory factors for recovery from stalled states and adaptation to environmental changes. Here, T. Kouba, J. Dohnálek, L. Krásný et.al.investigated the mechanism by which a helicase-like factor HelD recycles RNAP. They report a cryo-EM structure of a complex between the Mycobacterium smegmatis RNAP and HelD. The crescent-shaped HelD simultaneously penetrates deep into two RNAP channels that are responsible for nucleic acids binding and substrate delivery to the active site, thereby locking RNAP in an inactive state. They show that HelD prevents non-specific interactions between RNAP and DNA and dissociates stalled transcription elongation complexes. The liberated RNAP can either stay dormant, sequestered by HelD, or upon HelD release, restart transcription. Their results provide insights into the architecture and regulation of the highly medically-relevant mycobacterial transcription machinery and define HelD as a clearing factor that releases RNAP from nonfunctional complexes with nucleic acids.
Kouba, T., Koval’, T., Sudzinová, P., Pospíšil, J., Brezovská, B., Hnilicová, J., Šanderová, H., Janoušková, M., Šiková, M., Halada, P., Sýkora, M., Barvík, I., Nováček, J., Trundová, M., Dušková, J., Skálová, T., URee Chon, U.R., Murakami, K.S., Dohnálek, J., and Krásný, L.: Mycobacterial HelD is a nucleic acids-clearing factor for RNA polymerase, Nature Comm. (2020) 11, 6419, https://doi.org/10.1038/s41467-020-20158-4
literature to read, science to follow
In this section, a distinct selection of six highly stimulating research publications and reviews published during past 6 months is presented. It is our hope that links to exciting science, which deserves attention of the structural biology community, will help you to locate gems in the steadily expanding jungle of scientific literature. You are welcome to point out to any paper you found interesting by sending a link or citation to readerscorner@ciisb.org. The section is being updated regularly.
“Everything is theoretically impossible, until it is done.”
Robert A. Heinlein