Interplay between the host and influenza virus has a pivotal role for the outcome of infection.The matrix proteins M2/BM2 from influenza (A and B) viruses are small type III integral membrane proteins with a single transmembrane domain,a short amino-terminal ectodomain and a long carboxy-terminal cytoplasmic domain.They function as proton channels,mainly forming a membrane-spanning pore through the transmembrane domain tetramer,and are essential for virus assembly and release of the viral genetic materials in the endosomal fusion process.However,little is known about the host factors which interact with M2/BM2 proteins and the functions of the long cytoplasmic domain are currently unknown.Starting with yeast two-hybrid screening and applying a series of experiments we identified that the β1 subunit of the host Na+/K+-ATPase β1 subunit (ATP1B1) interacts with the cytoplasmic domain of both the M2 and BM2 proteins.A stable ATP1B1 knockdown MDCK cell line was established and we showed that the ATP1B1 knockdown suppressed influenza virus A/WSN/33 replication,implying that the interaction is crucial for influenza virus replication in the host cell.We propose that influenza virus M2/BM2 cytoplasmic domain has an important role in the virus-host interplay and facilitates virus replication.
Human NUDT16(hNUDT16)is a decapping enzyme initially identified as the human homolog to the Xenopus laevis X29.As a metalloenzyme,hNUDT16 relies on divalent cations for its cap-hydrolysis activity to remove m7 GDP and m227GDP from RNAs.Metal also determines substrate specificity of the enzyme.So far,only U8 small nucleolar RNA(snoRNA)has been identified as the substrate of hNUDT16 in the presence of Mg2+.Here we demonstrate that besides U8,hNUDT16 can also actively cleave the m7 GDP cap from mRNAs in the presence of Mg2+or Mn2+.We further show that hNUDT16 does not preferentially recognize U8 or mRNA substrates by our cross-inhibition and quantitative decapping assays.In addition,our mutagenesis analysis identifies several key residues involved in hydrolysis and confirms the key role of the REXXEE motif in catalysis.Finally an investigation into the subcellular localization of hNUDT16 revealed its abundance in both cytoplasm and nucleus.These findings extend the substrate spectrum of hNUDT16 beyond snoRNAs to also include mRNA,demonstrating the pleiotropic decapping activity of hNUDT16.
