title: Structure of Hjc, a Holliday junction resolvase, from Sulfolobus solfataricus.
abstract: The 2.15-A structure of Hjc, a Holliday junction-resolving enzyme from the archaeon Sulfolobus solfataricus, reveals extensive structural homology with a superfamily of nucleases that includes type II restriction enzymes. Hjc is a dimer with a large DNA-binding surface consisting of numerous basic residues surrounding the metal-binding residues of the active sites. Residues critical for catalysis, identified on the basis of sequence comparisons and site-directed mutagenesis studies, are clustered to produce two active sites in the dimer, about 29 A apart, consistent with the requirement for the introduction of paired nicks in opposing strands of the four-way DNA junction substrate. Hjc displays similarity to the restriction endonucleases in the way its specific DNA-cutting pattern is determined but uses a different arrangement of nuclease subunits. Further structural similarity to a broad group of metal/phosphate-binding proteins, including conservation of active-site location, is observed. A high degree of conservation of surface electrostatic character is observed between Hjc and T4-phage endonuclease VII despite a complete lack of structural homology. A model of the Hjc-Holliday junction complex is proposed, based on the available functional and structural data.
authors.affiliation: Wellcome Trust Biocentre, University of Dundee, Dundee, Tayside DD1 5EH, United Kingdom. C.S.Bond@dundee.ac.uk
authors.forename: C S
authors.initials: CS
authors.lastname: Bond
authors.forename: M
authors.initials: M
authors.lastname: Kvaratskhelia
authors.forename: D
authors.initials: D
authors.lastname: Richard
authors.forename: M F
authors.initials: MF
authors.lastname: White
authors.forename: W N
authors.initials: WN
authors.lastname: Hunter
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D019281:Dimerization; D004706:Endodeoxyribonucleases / Q000737:chemistry*; D045565:Holliday Junction Resolvases; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016944:Sulfolobus / Q000201:enzymology*
chemical_list: D004706:Endodeoxyribonucleases; D045565:Holliday Junction Resolvases