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PDBsum entry 3ec2
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References listed in PDB file
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Key reference
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Title
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Structural synergy and molecular crosstalk between bacterial helicase loaders and replication initiators.
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Authors
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M.L.Mott,
J.P.Erzberger,
M.M.Coons,
J.M.Berger.
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Ref.
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Cell, 2008,
135,
623-634.
[DOI no: ]
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PubMed id
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Abstract
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The loading of oligomeric helicases onto replication origins marks an essential
step in replisome assembly. In cells, dedicated AAA+ ATPases regulate loading,
however, the mechanism by which these factors recruit and deposit helicases has
remained unclear. To better understand this process, we determined the structure
of the ATPase region of the bacterial helicase loader DnaC from Aquifex aeolicus
to 2.7 A resolution. The structure shows that DnaC is a close paralog of the
bacterial replication initiator, DnaA, and unexpectedly shares an ability to
form a helical assembly similar to that of ATP-bound DnaA. Complementation and
ssDNA-binding assays validate the importance of homomeric DnaC interactions,
while pull-down experiments show that the DnaC and DnaA AAA+ domains interact in
a nucleotide-dependent manner. These findings implicate DnaC as a molecular
adaptor that uses ATP-activated DnaA as a docking site for regulating the
recruitment and correct spatial deposition of the DnaB helicase onto origins.
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Figure 1.
Figure 1. Structure of DnaC[AAA+]
(A) Domain
representation of DnaC. The N-terminal helicase binding region
is colored gray and the central AAA+ domain is shown in red.
Numbers refer to amino acid positions. AAA+ motifs are
highlighted. WA, Walker-A; WB, Walker-B; SI, sensor-I; SII,
sensor-II; ISM, Initiator Specific Motif.
(B) Sequence
alignment of selected DnaC and DnaA homologs. Alignment was
generated by ClustalX (Thompson et al., 1997).
(C) Stereo
view of DnaC[AAA+]. Walker-A and -B motifs are blue and yellow,
respectively. The sensor-I residue is green and the Box VII
helix cyan. ADP and the coordinating magnesium ion (black) are
shown within the ATP binding cleft. An internal disordered
region is shown as a dotted line. This and all other molecular
figures were generated with PyMOL (pymol.sourceforge.net).
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Figure 6.
Figure 6. Model for DnaC/DnaA Crosstalk and Helicase
Deposition
(A) Structural model for oligomeric DnaC:DnaA
interactions. The figure was generated by superimposing the last
subunit of a six-subunit DnaC[AAA+] oligomer onto the end of a
twelve-subunit DnaA filament assembly. Axial and side views are
shown. Cyan spheres represent bound nucleotide.
(B) Model
for the symmetric loading of two replicative helicases at oriC.
Left: DnaA assembles at oriC and melts the DUE (purple strands).
Middle, (1): helicase loading on the bottom DUE strand is
facilitated through direct DnaA:DnaB interaction. Middle, (2):
DnaC, through a specific interaction with ATP-charged DnaA,
recruits the helicase destined for the top strand to oriC.
Right: ATP hydrolysis and loss of DnaC frees both DnaB hexamers
to migrate to their proper fork positions.
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The above figures are
reprinted
from an Open Access publication published by Cell Press:
Cell
(2008,
135,
623-634)
copyright 2008.
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