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Crystal structure of the mRNA export receptor NXF1/NXT1 in complex with influenza virus NS1 proteinCrystal structure of the mRNA export receptor NXF1/NXT1 in complex with influenza virus NS1 protein
Structural highlights
Function[I7CAR2_9INFA] Inhibits post-transcriptional processing of cellular pre-mRNA, by binding and inhibiting two cellular proteins that are required for the 3'-end processing of cellular pre-mRNAs: the 30 kDa cleavage and polyadenylation specificity factor/CPSF4 and the poly(A)-binding protein 2/PABPN1. In turn, unprocessed 3' end pre-mRNAs accumulate in the host nucleus and are no longer exported to the cytoplasm. Cellular protein synthesis is thereby shut off very early after virus infection. Viral protein synthesis is not affected by the inhibition of the cellular 3' end processing machinery because the poly(A) tails of viral mRNAs are produced by the viral polymerase through a stuttering mechanism.[RuleBase:RU362113][SAAS:SAAS01036581] Prevents the establishment of the cellular antiviral state by inhibiting TRIM25-mediated DDX58 ubiquitination, which normally triggers the antiviral transduction signal that leads to the activation of type I IFN genes by transcription factors IRF3 and IRF7. Prevents human EIF2AK2/PKR activation, either by binding double-strand RNA, or by interacting directly with EIF2AK2/PKR. This function may be important at the very beginning of the infection, when NS1 is mainly present in the cytoplasm. Also binds poly(A) and U6 snRNA.[RuleBase:RU362113][SAAS:SAAS01036591] [NXF1_HUMAN] Involved in the nuclear export of mRNA species bearing retroviral constitutive transport elements (CTE) and in the export of mRNA from the nucleus to the cytoplasm. The NXF1-NXT1 heterodimer is involved in the export of HSP70 mRNA in conjunction with ALYREF/THOC4 and THOC5.[1] [2] [NXT1_HUMAN] Stimulator of protein export for NES-containing proteins. Also plays a role in the nuclear export of U1 snRNA, tRNA, and mRNA. The NXF1-NXT1 heterodimer is involved in the export of HSP70 mRNA in conjunction with ALYREF/THOC4 and THOC5.[3] [4] [5] [6] Publication Abstract from PubMedInfluenza viruses antagonize key immune defence mechanisms via the virulence factor non-structural protein 1 (NS1). A key mechanism of virulence by NS1 is blocking nuclear export of host messenger RNAs, including those encoding immune factors(1-3); however, the direct cellular target of NS1 and the mechanism of host mRNA export inhibition are not known. Here, we identify the target of NS1 as the mRNA export receptor complex, nuclear RNA export factor 1-nuclear transport factor 2-related export protein 1 (NXF1-NXT1), which is the principal receptor mediating docking and translocation of mRNAs through the nuclear pore complex via interactions with nucleoporins(4,5). We determined the crystal structure of NS1 in complex with NXF1-NXT1 at 3.8 A resolution. The structure reveals that NS1 prevents binding of NXF1-NXT1 to nucleoporins, thereby inhibiting mRNA export through the nuclear pore complex into the cytoplasm for translation. We demonstrate that a mutant influenza virus deficient in binding NXF1-NXT1 does not block host mRNA export and is attenuated. This attenuation is marked by the release of mRNAs encoding immune factors from the nucleus. In sum, our study uncovers the molecular basis of a major nuclear function of influenza NS1 protein that causes potent blockage of host gene expression and contributes to inhibition of host immunity. Structural basis for influenza virus NS1 protein block of mRNA nuclear export.,Zhang K, Xie Y, Munoz-Moreno R, Wang J, Zhang L, Esparza M, Garcia-Sastre A, Fontoura BMA, Ren Y Nat Microbiol. 2019 Oct;4(10):1671-1679. doi: 10.1038/s41564-019-0482-x. Epub, 2019 Jul 1. PMID:31263181[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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