title: The structure of a birnavirus polymerase reveals a distinct active site topology.
abstract: Single-subunit polymerases are universally encoded in both cellular organisms and viruses. Their three-dimensional structures have the shape of a right-hand with the active site located in the palm region, which has a topology similar to that of the RNA recognition motif (RRM) found in many RNA-binding proteins. Considering that polymerases have well conserved structures, it was surprising that the RNA-dependent RNA polymerases from birnaviruses, a group of dsRNA viruses, have their catalytic motifs arranged in a permuted order in sequence. Here we report the 2.5 A structure of a birnavirus VP1 in which the polymerase palm subdomain adopts a new active site topology that has not been previously observed in other polymerases. In addition, the polymerase motif C of VP1 has the sequence of -ADN-, a highly unusual feature for RNA-dependent polymerases. Through site-directed mutagenesis, we have shown that changing the VP1 motif C from -ADN- to -GDD- results in a mutant with an increased RNA synthesis activity. Our results indicate that the active site topology of VP1 may represent a newly developed branch in polymerase evolution, and that birnaviruses may have acquired the -ADN- mutation to control their growth rate.
authors: Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77005, USA.
authors: Junhua
authors: J
authors: Pan
authors: Vikram N
authors: VN
authors: Vakharia
authors: Yizhi Jane
authors: YJ
authors: Tao
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D005075:Biological Evolution; D018059:Birnaviridae / Q000201:enzymology*; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D012324:RNA-Dependent RNA Polymerase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D012313:RNA; D012324:RNA-Dependent RNA Polymerase