title: Hexameric ring structure of the full-length archaeal MCM protein complex.
abstract: In eukaryotes, a family of six homologous minichromosome maintenance (MCM) proteins has a key function in ensuring that DNA replication occurs only once before cell division. Whereas all eukaryotes have six paralogues, in some Archaea a single protein forms a homomeric assembly. The complex is likely to function as a helicase during DNA replication. We have used electron microscopy to obtain a three-dimensional reconstruction of the full-length MCM from Methanobacterium thermoautotrophicum. Six monomers are arranged around a sixfold axis, generating a ring-shaped molecule with a large central cavity and lateral holes. The channel running through the molecule can easily accommodate double-stranded DNA. The crystal structure of the amino-terminal fragment of MCM and a model for the AAA+ hexamer have been docked into the map, whereas additional electron density suggests that the carboxy-terminal domain is located at the interface between the two domains. The structure suggests that the MCM complex is likely to act in a different manner to traditional hexameric helicases and is likely to bear more similarity to the SV40 large T antigen or to double-stranded DNA translocases.
authors.affiliation: Department of Biological Sciences, Imperial College, London SW7 2AZ, UK.
authors.forename: Tillmann
authors.initials: T
authors.lastname: Pape
authors.forename: Hedije
authors.initials: H
authors.lastname: Meka
authors.forename: Shaoxia
authors.initials: S
authors.lastname: Chen
authors.forename: Giorgia
authors.initials: G
authors.lastname: Vicentini
authors.forename: Marin
authors.initials: M
authors.lastname: van Heel
authors.forename: Silvia
authors.initials: S
authors.lastname: Onesti
mesh_terms: D001105:Archaea / Q000737:chemistry*; D019843:Archaeal Proteins / Q000737:chemistry*; D004265:DNA Helicases / Q000737:chemistry*; D008854:Microscopy, Electron; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D019843:Archaeal Proteins; D004265:DNA Helicases; C403162:MCM protein, Methanobacterium thermoautotrophicum