4eqk | pdb_00004eqk
Crystal structure of the cap-binding domain of polymerase basic protein 2 from influenza virus A/Hong Kong/1/68 (h3n2) with bound m7GTP
Structural highlights
FunctionPB2_I68A4 Involved in transcription initiation and cap-stealing mechanism, in which cellular capped pre-mRNA are used to generate primers for viral transcription. Binds the cap of the target pre-RNA which is subsequently cleaved by PB1. May play a role in genome replication (By similarity). 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. See AlsoReferences
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