title: Structural basis for DNA duplex separation by a superfamily-2 helicase.
abstract: To reveal the mechanism of processive strand separation by superfamily-2 (SF2) 3'-->5' helicases, we determined apo and DNA-bound crystal structures of archaeal Hel308, a helicase that unwinds lagging strands and is related to human DNA polymerase theta. Our structure captures the duplex-unwinding reaction, shows that initial strand separation does not require ATP and identifies a prominent beta-hairpin loop as the unwinding element. Similar loops in hepatitis C virus NS3 helicase and RNA-decay factors support the idea that this duplex-unwinding mechanism is applicable to a broad subset of SF2 helicases. Comparison with ATP-bound SF2 enzymes suggests that ATP promotes processive unwinding of 1 base pair by ratchet-like transport of the 3' product strand. Our results provide a first structural framework for strand separation by processive SF2 3'-->5' helicases and reveal important mechanistic differences from SF1 helicases.
authors.affiliation: Center for Integrated Protein Science, Gene Center and Department of Chemistry and Biochemistry, Ludwig-Maximilians-University Munich, Feodor-Lynen-Str. 25, 81377 Munich, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Büttner
authors.forename: Sebastian
authors.initials: S
authors.lastname: Nehring
authors.forename: Karl-Peter
authors.initials: KP
authors.lastname: Hopfner
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry*; D019611:Archaeoglobus fulgidus / Q000201:enzymology*; D001483:Base Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry; D004265:DNA Helicases / Q000737:chemistry*; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D011487:Protein Conformation
chemical_list: D019843:Archaeal Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D004265:DNA Helicases