title: Crystal structure of the hexameric replicative helicase RepA of plasmid RSF1010.
abstract: Unwinding of double-stranded DNA into single-stranded intermediates required for various fundamental life processes is catalyzed by helicases, a family of mono-, di- or hexameric motor proteins fueled by nucleoside triphosphate hydrolysis. The three-dimensional crystal structure of the hexameric helicase RepA encoded by plasmid RSF1010 has been determined by X-ray diffraction at 2.4 A resolution. The hexamer shows an annular structure with 6-fold rotational symmetry and a approximately 17 A wide central hole, suggesting that single-stranded DNA may be threaded during unwinding. Homologs of all five conserved sequence motifs of the DnaB-like helicase family are found in RepA, and the topography of the monomer resembles RecA and the helicase domain of the bacteriophage T7 gp4 protein. In a modeled complex, ATP molecules are located at the subunit interfaces and clearly define adenine-binding and ATPase catalytic sites formed by amino acid residues located on adjacent monomers; most remarkable is the "arginine finger" Arg207 contributing to the active site in the adjacent monomer. This arrangement of active-site residues suggests cooperativity between monomers in ATP hydrolysis and helicase activity of RepA. The mechanism of DNA unwinding remains elusive, as RepA is 6-fold symmetric, contrasting the recently published asymmetric structure of the bacteriophage T7 gp4 helicase domain.
authors.affiliation: Institut für Kristallographie, Freie Universität Berlin, Takustr. 6, Berlin, D-14195, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Niedenzu
authors.forename: D
authors.initials: D
authors.lastname: Röleke
authors.forename: G
authors.initials: G
authors.lastname: Bains
authors.forename: E
authors.initials: E
authors.lastname: Scherzinger
authors.forename: W
authors.initials: W
authors.lastname: Saenger
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019915:DNA Primase / Q000737:chemistry; D004268:DNA-Binding Proteins; D019281:Dimerization; D006090:Gram-Negative Bacteria / Q000201:enzymology* / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015534:Trans-Activators
chemical_list: D004268:DNA-Binding Proteins; D021122:Protein Subunits; D011506:Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; C045264:replication initiator protein; D000255:Adenosine Triphosphate; D001120:Arginine; D019915:DNA Primase; D000251:Adenosine Triphosphatases; D004265:DNA Helicases