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Crystal structure of the cap-binding domain of polymerase basic protein 2 from influenza virus A/Bar-headed Gs/Qinghai/15c/2005 (h5n1) with bound m7GTP
Structural highlights
FunctionQ4FAU9_9INFA Plays an essential role in transcription initiation and cap-stealing mechanism, in which cellular capped pre-mRNAs are used to generate primers for viral transcription. Recognizes and binds the 7-methylguanosine-containing cap of the target pre-RNA which is subsequently cleaved after 10-13 nucleotides by the viral protein PA. Plays a role in the initiation of the viral genome replication and modulates the activity of the ribonucleoprotein (RNP) complex. In addition, participates in the inhibition of type I interferon induction through interaction with and inhibition of the host mitochondrial antiviral signaling protein MAVS.[HAMAP-Rule:MF_04062] Publication Abstract from PubMedInfluenza virus RNA-dependent RNA polymerase is a heterotrimer composed of PA, PB1, and PB2 subunits. RNA-dependent RNA polymerase is required for both transcription and replication of influenza viral RNA taking place in the nucleus of infected cells. A "cap-snatching" mechanism is used to generate a 5'-capped primer for transcription in which the cap-binding domain of PB2 (PB2cap) captures the 5' cap of the host pre-mRNA. Our statistical analysis of PB2 sequences showed that residue Lys(339) located in the cap-binding pocket of H5N1 PB2cap was gradually replaced by Thr(339) over the past decade. To understand the role of this amino acid polymorphism, we solved the crystal structures of PB2cap with or without a pre-mRNA cap analog, m(7)GTP, in the presence of Lys(339) or Thr(339). The structures showed that Lys(339) contributes to binding the gamma-phosphate group of m(7)GTP, and the replacement of Lys(339) by Thr eliminates this interaction. Isothermal titration calorimetry analysis showed that Thr(339) attenuated the PB2cap cap binding activity in vitro compared with Lys(339). Further functional studies confirmed that Thr(339)-PB2-containing ribonucleoprotein complex has a reduced influenza polymerase activity and RNA synthesis activity, and a reconstituted H5N1 virus containing the Thr(339) substitution exhibited a lower virulence to mice but more active replication in Madin-Darby canine kidney cells. The K339T substitution in the cap-binding pocket of PB2 modulates the polymerase activity and virulence by regulating the cap binding activity. It is informative to track variations in the cap-binding pocket of PB2 in surveillance of the evolution and spread of influenza virus. Structural and functional characterization of K339T substitution identified in the PB2 subunit cap-binding pocket of influenza A virus.,Liu Y, Qin K, Meng G, Zhang J, Zhou J, Zhao G, Luo M, Zheng X J Biol Chem. 2013 Apr 19;288(16):11013-23. doi: 10.1074/jbc.M112.392878. Epub, 2013 Feb 22. PMID:23436652[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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