Hexameric ring structure of the full-length archaeal MCM protein complex.
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.
Pape
Tillmann
T
Department of Biological Sciences, Imperial College, London SW7 2AZ, UK.
Meka
Hedije
H
Chen
Shaoxia
S
Vicentini
Giorgia
G
van Heel
Marin
M
Onesti
Silvia
S
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
D019843:Archaeal Proteins; D004265:DNA Helicases; C403162:MCM protein, Methanobacterium thermoautotrophicum