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X-ray structure of full-length H6N6 NS1
Structural highlights
FunctionQ20NS3_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). This results in the accumulation of unprocessed 3' end pre-mRNAs which can't be exported from the nucleus. 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 (By similarity).[SAAS:SAAS000256_004_252803] 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 like 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. Suppresses the RNA silencing-based antiviral response in Drosophila cells (By similarity).[SAAS:SAAS000256_004_198562] Publication Abstract from PubMedNS1 of influenza A virus is a potent antagonist of host antiviral interferon responses. This multifunctional protein with two distinctive domains, a RNA binding domain (RBD) and an effector domain (ED) separated by a linker region (LR), is implicated in replication, pathogenesis and host range. Although the structures of individual domains of NS1 from different strains of influenza viruses have been reported, the only structure of full-length NS1 available to date is from a H5N1 strain (A/Vietnam/1203/2004). By carrying out crystallographic analyses of full-length H6N6-NS1 (A/blue-winged teal/MN/993/1980) and a LR deletion mutant, combined with mutational analysis, we show here that these full-length NS1 structures provide an exquisite structural sampling of various conformational states of NS1 that based on the orientation of the ED with respect to RBD can be summarized as 'open', 'semi-open' and 'closed' conformations. Our studies show that preference for these states is clearly dictated by determinants such as linker length, residue composition at position 71, and a mechanical hinge, providing a structural basis for strain-dependent functional variations in NS1. Because of the flexibility inherent in the LR, any particular NS1 could sample the conformational space around these states to engage ED in different quaternary interactions so that it may participate in specific protein-protein or protein-RNA interactions to allow for the known multi-functionality of NS1. We propose that such conformational plasticity provides a mechanism for auto-regulating NS1 functions, depending on its temporal distribution, post-translational modifications, and nuclear or cellular localization, during the course of virus infection.IMPORTANCE NS1 of influenza A virus is a multifunctional protein associated with numerous strain-specific regulatory functions during viral infection, including conferring resistance to antiviral interferon induction, replication, pathogenesis, virulence and host range. NS1 has two domains, a RNA binding domain and an effector domain separated by a linker. To date, the only full-length NS1 structure available is that from a H5N1 strain (A/Vietnam/1203/2004). Here, we determined crystal structures of wildtype and linker region mutant of the H6N6 NS1 (A/blue-winged teal/MN/993/1980), which together with the previously determined H5N1 NS1 structure show that NS1 exhibits significant strain-dependent structural polymorphism due to variations in linker length, residue composition at position 71, and a mechanical hinge. Such a structural polymorphism may be the basis for strain-specific functions associated with NS1. The influenza A virus protein NS1 displays structural polymorphism.,Carrillo B, Choi JM, Bornholdt ZA, Sankaran B, Rice AP, Prasad BV J Virol. 2014 Jan 29. PMID:24478439[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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