key: cord-0714245-hcysdxju
authors: Vann, Kendra R.; Tencer, Adam H.; Kutateladze, Tatiana G.
title: Inhibition of translation and immune responses by the virulence factor Nsp1 of SARS-CoV-2
date: 2020-10-09
journal: Signal Transduct Target Ther
DOI: 10.1038/s41392-020-00350-0
sha: 1701953d230d2accd43331c5d0316eb1ac85f9f9
doc_id: 714245
cord_uid: hcysdxju

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To understand the molecular basis of the Nsp1 function, Thoms et al. 1 determined the cryo-EM structures of Nsp1 in complex with human ribosomal 40S and 80S subunits. The structures were refined to a high 2.6 Å average resolution, allowing for detailed analysis of the complexes and elucidating key contacts and the overall mechanism underlying inhibition of mRNA translation by Nsp1. In the Nsp1:40S complex, two C-terminal α-helices of Nsp1 (colored red in Fig. 1a ) insert into the mRNA entry channel. The first α-helix (residues 154-160 of Nsp1) interacts with the ribosomal proteins uS3 and uS5 (colored light blue and light green, respectively, in Fig. 1b) , whereas the second α-helix (residues 166-179 of Nsp1) interacts with uS5 and ribosomal rRNA h18. The structure also reveals that the two helices are stabilized through hydrophobic interactions. The HK motif of Nsp1 is located in the loop between the two helices and forms important contacts with rRNA h18. Specifically, K164 of Nsp1 occupies the negatively charged pocket formed by the backbone phosphates of G625 and U630 of rRNA, whereas H165 is stacked between U607 and U630. Overall, a high degree of complementarity in electrostatics and shape between the two helices of Nsp1 and the mRNA channel of the ribosomal subunit allowed Nsp1 to act as a plug, which effectively obstructs the mRNA entry channel. Independently, based on the cryo-EM structure of Nsp1 bound to the ribosomal 40S subunit, Schubert et al. 2 came to a similar conclusion that Nsp1 inhibits translation by sterically occluding the mRNA channel entrance and interfering with the binding of the host mRNA.

Blocking the host mRNA translation machinery impedes production of the proteins necessary for anti-viral defense and other normal cell functions. Thoms et al. 1 show that Nsp1 almost completely prevents translation of interferons IFN-β and IFN-λ1 and interleukin-8, as well as interferon stimulated anti-viral factors. Mutation of the Nsp1 KH motif restored the innate immune response in infected cells, further pointing to the vital role of the Nsp1 C-terminal helices in disabling the host cell anti-viral defense system.

Considering the ability of Nsp1 to substantially downregulate the innate immune responses, this virulence factor could become another appealing drug target in addition to the Spike protein and the RNA polymerase Nsp12 of SARS-CoV-2. 3-5 Identification of compounds that bind and impair the C-terminal helices of Nsp1 or the N-terminal domain of Nsp1 can be an important new treatment strategy. Further research is also needed to determine whether Nsp1 can be used for the development of a vaccine. Lastly, to better understand the SARS-CoV-2 pathogenesis, it is essential to identify the mechanism by which SARS-CoV-2 Fig. 1 Structural basis for binding of the SARS-CoV-2 Nsp1 protein to the ribosomal 40S subunit. a Domain architecture of the SARS-CoV-2 Nsp1 protein (top). The N-terminal domain (NTD) and the C-terminal α-helices are labeled and colored light blue and red, respectively. Cryo-EM structure of the Nsp1 protein bound to 40S (PDB 6zlw) (bottom). The two C-terminal α-helices of Nsp1 (red) insert into the mRNA entry channel of 40S (gray). The resolution of the NTD region of Nsp1 in the cryo-EM density map was insufficient to unambiguously identify this domain. b Close view of the interface of the 40S:Nsp1 complex (PDB 6zlw). The two C-terminal α-helices of Nsp1 (red) make contacts with ribosomal rRNA h18 (orange phosphate backbone and blue nucleotide bases) and with the ribosomal proteins uS3 (light blue) and uS5 (light green). The K164 and H165 residues of the KH motif of Nsp1 are shown as red sticks

Structural basis for translational shutdown and immune evasion by the Nsp1 protein of SARS-CoV-2

CoV-2 Nsp1 binds ribosomal mRNA channel to inhibit translation

Research in the Kutateladze laboratory is funded by the NIH.

K.R.V., A.H.T., and T.G.K. contributed to the writing of this manuscript.

Competing interests: The authors declare no competing interests.

produces its own viral proteins, overcoming the Nsp1-mediated host mRNA translation shutdown. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons. org/licenses/by/4.0/. Author :-The following queries have arisen during the editing of your manuscript. Please answer by making the requisite corrections directly in the e.proofing tool rather than marking them up on the PDF. This will ensure that your corrections are incorporated accurately and that your paper is published as quickly as possible.

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