title: Crystal structure of the eukaryotic origin recognition complex.
abstract: Initiation of cellular DNA replication is tightly controlled to sustain genomic integrity. In eukaryotes, the heterohexameric origin recognition complex (ORC) is essential for coordinating replication onset. Here we describe the crystal structure of Drosophila ORC at 3.5 Å resolution, showing that the 270 kilodalton initiator core complex comprises a two-layered notched ring in which a collar of winged-helix domains from the Orc1-5 subunits sits atop a layer of AAA+ (ATPases associated with a variety of cellular activities) folds. Although canonical inter-AAA+ domain interactions exist between four of the six ORC subunits, unanticipated features are also evident. These include highly interdigitated domain-swapping interactions between the winged-helix folds and AAA+ modules of neighbouring protomers, and a quasi-spiral arrangement of DNA binding elements that circumnavigate an approximately 20 Å wide channel in the centre of the complex. Comparative analyses indicate that ORC encircles DNA, using its winged-helix domain face to engage the mini-chromosome maintenance 2-7 (MCM2-7) complex during replicative helicase loading; however, an observed out-of-plane rotation of more than 90° for the Orc1 AAA+ domain disrupts interactions with catalytic amino acids in Orc4, narrowing and sealing off entry into the central channel. Prima facie, our data indicate that Drosophila ORC can switch between active and autoinhibited conformations, suggesting a novel means for cell cycle and/or developmental control of ORC functions.
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Franziska
authors.initials: F
authors.lastname: Bleichert
authors.affiliation: Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California 94720, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Botchan
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Berger
mesh_terms: D000818:Animals; D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004261:DNA Replication; D004331:Drosophila melanogaster / Q000737:chemistry*; D005057:Eukaryotic Cells / Q000737:chemistry*; D064110:Minichromosome Maintenance Proteins / Q000737:chemistry / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D051738:Origin Recognition Complex / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012399:Rotation
chemical_list: D019843:Archaeal Proteins; D051738:Origin Recognition Complex; D021122:Protein Subunits; D004247:DNA; D064110:Minichromosome Maintenance Proteins