title: The Methanobacterium thermoautotrophicum MCM protein can form heptameric rings.
abstract: Mini-chromosome maintenance (MCM) proteins form a conserved family found in all eukaryotes and are essential for DNA replication. They exist as heteromultimeric complexes containing as many as six different proteins. These complexes are believed to be the replicative helicases, functioning as hexameric rings at replication forks. In most archaea a single MCM protein exists. The protein from Methanobacterium thermoautotrophicum (mtMCM) has been reported to assemble into a large complex consistent with a dodecamer. We show that mtMCM can assemble into a heptameric ring. This ring contains a C-terminal helicase domain that can be fit with crystal structures of ring helicases and an N-terminal domain of unknown function. While the structure of the ring is very similar to that of hexameric replicative helicases such as bacteriophage T7 gp4, our results show that such ring structures may not be constrained to have only six subunits.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, Va 22908, USA.
authors.forename: Xiong
authors.initials: X
authors.lastname: Yu
authors.forename: Margaret S
authors.initials: MS
authors.lastname: VanLoock
authors.forename: Andrzej
authors.initials: A
authors.lastname: Poplawski
authors.forename: Zvi
authors.initials: Z
authors.lastname: Kelman
authors.forename: Tao
authors.initials: T
authors.lastname: Xiang
authors.forename: Bik K
authors.initials: BK
authors.lastname: Tye
authors.forename: Edward H
authors.initials: EH
authors.lastname: Egelman
mesh_terms: D020816:Amino Acid Motifs; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D004247:DNA / Q000096:biosynthesis; D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D017014:Methanobacterium / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008958:Models, Molecular; D017434:Protein Structure, Tertiary
chemical_list: D019843:Archaeal Proteins; D004247:DNA; D004265:DNA Helicases; C403162:MCM protein, Methanobacterium thermoautotrophicum