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PDBsum entry 3f9v
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References listed in PDB file
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Key reference
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Title
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Crystal structure of a near-Full-Length archaeal mcm: functional insights for an aaa+ hexameric helicase.
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Authors
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A.S.Brewster,
G.Wang,
X.Yu,
W.B.Greenleaf,
J.M.Carazo,
M.Tjajadia,
M.G.Klein,
X.S.Chen.
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Ref.
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Proc Natl Acad Sci U S A, 2008,
105,
20191-20196.
[DOI no: ]
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PubMed id
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Abstract
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The minichromosome maintenance protein (MCM) complex is an essential replicative
helicase for DNA replication in Archaea and Eukaryotes. Whereas the eukaryotic
complex consists of 6 homologous proteins (MCM2-7), the archaeon Sulfolobus
solfataricus has only 1 MCM protein (ssoMCM), 6 subunits of which form a
homohexamer. Here, we report a 4.35-A crystal structure of the near-full-length
ssoMCM. The structure shows an elongated fold, with 5 subdomains that are
organized into 2 large N- and C-terminal domains. A near-full-length ssoMCM
hexamer generated based on the 6-fold symmetry of the N-terminal
Methanothermobacter thermautotrophicus (mtMCM) hexamer shows intersubunit
distances suitable for bonding contacts, including the interface around the ATP
pocket. Four unusual beta-hairpins of each subunit are located inside the
central channel or around the side channels in the hexamer. Additionally, the
hexamer fits well into the double-hexamer EM map of mtMCM. Our mutational
analysis of residues at the intersubunit interfaces and around the side channels
demonstrates their critical roles for hexamerization and helicase function.
These structural and biochemical results provide a basis for future study of the
helicase mechanisms of the archaeal and eukaryotic MCM complexes in DNA
replication.
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Figure 2.
Structural features of the ssoMCM hexamer. (A) Double
hexameric EM map of mtMCM with the ssoMCM hexamer model fitting
snugly inside the map (20). The PS1 hairpin is located near the
side channels of the EM map (indicated by an arrow). (B) Side
and top views of the ssoMCM hexamer model. Subunits are labeled
a–f. Two subunits in the front are removed in the side view to
reveal the interior. The 4 β-hairpins located inside the
central and side channels are colored. (C) Close-up view of
subunits a and b in the back side of the hexamer in B (side
view). β-Hairpins are labeled as in Fig. 1B. The opening
between the 2 neighboring subunits at the C terminus (side
channel) is indicated. (D) Close-up top view as in B, showing
the radial and helical nature of the 4 β-hairpins.
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Figure 4.
Two possible DNA unwinding modes by MCM helicase. (A)
Schematic representation of a MCM hexamer helicase. The 4
β-hairpins (NT, H2I, PS1, and EXT hairpins) are represented by
short solid bars; the central channel and the side channels are
in darker shades. (B) Steric exclusion model for a
single-hexameric MCM helicase. (C) Side-channel extrusion model,
showing ssDNA extruding from the side channel. DNA is shown as
black lines. Arrows indicate direction of helicase movement.
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