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PDBsum entry 3euk
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442 a.a.
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455 a.a.
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101 a.a.
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124 a.a.
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173 a.a.
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107 a.a.
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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 studies of a bacterial condensin complex reveal ATP-Dependent disruption of intersubunit interactions.
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Authors
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J.S.Woo,
J.H.Lim,
H.C.Shin,
M.K.Suh,
B.Ku,
K.H.Lee,
K.Joo,
H.Robinson,
J.Lee,
S.Y.Park,
N.C.Ha,
B.H.Oh.
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Ref.
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Cell, 2009,
136,
85-96.
[DOI no: ]
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PubMed id
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Abstract
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Condensins are key mediators of chromosome condensation across organisms. Like
other condensins, the bacterial MukBEF condensin complex consists of an SMC
family protein dimer containing two ATPase head domains, MukB, and two
interacting subunits, MukE and MukF. We report complete structural views of the
intersubunit interactions of this condensin along with ensuing studies that
reveal a role for the ATPase activity of MukB. MukE and MukF together form an
elongated dimeric frame, and MukF's C-terminal winged-helix domains (C-WHDs)
bind MukB heads to constitute closed ring-like structures. Surprisingly, one of
the two bound C-WHDs is forced to detach upon ATP-mediated engagement of MukB
heads. This detachment reaction depends on the linker segment preceding the
C-WHD, and mutations on the linker restrict cell growth. Thus ATP-dependent
transient disruption of the MukB-MukF interaction, which creates openings in
condensin ring structures, is likely to be a critical feature of the functional
mechanism of condensins.
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Figure 3.
Figure 3. Formation of the Asymmetric
hMukE–hMukF(M+C)–(hMukBhd^EQ–ATPγS)[2] Dimer
(A)
Structure of the asymmetric dimer in the Form II crystal. Only
one C-WHD of hMukF is bound to dimerized MukB heads. In the
inset, the 2F[o]-F[c] map calculated with the final refined
model highlights the electron density for the linker segment
preceding α1.
(B) Structural superposition. The C-WHDs of
MukF in the asymmetric dimer (red) and the symmetric dimer
(pink) in the Form I crystal are superposed. A circle highlights
that α1 in the asymmetric dimer is longer than that in the
symmetric dimer. The linker segment in the asymmetric dimer
overlaps with one MukF C-WHD in the symmetric dimer.
(C)
Detachment of hMukE–hMukF(M+C) from dimerized MukB heads in
solution. A sample containing 4 μM
hMukE–hMukF(M+C)–hMukBhd^EQ (band a) was reacted with 2 mM
ATP and visualized on a native gel. The mixture was partially
separated with a Superdex 200 column, and the chromatogram is
shown along with the size marker positions. The eluted
fractions, indicated by a double-headed arrow, were visualized
on a native and a denaturing gel, showing that bands b and c
correspond to high- and low-molecular weight species,
respectively. Band c is assigned to detached hMukE–hMukF(M+C)
according to the same band position of purified
hMukE–hMukF(M+C) (labeled as “Con”). By subtraction, band
b is assigned to hMukE–hMukF(M+C)–(hMukBhd^EQ–ATP)[2],
which was confirmed by quantification of the band intensities
for lane 1 of the denaturing gel ([hMukBhd^EQ]/[hMukE dimer] =
 vert,
similar 1.7). Accordingly, the minor species present in the
unreacted sample is identified as copurified asymmetric dimer
resulting from very low catalytic activity of hMukBhd^EQ. The
observed conversion reaction is schematically illustrated.
(D) Control experiments. Triple complexes between MukE,
MukF(M+C) and the indicated head domain of MukB were analyzed by
native gel electrophoresis. Left: Catalytically active
MukE–MukF(M+C)–MukBhd in reacting with 2 mM AMPPNP produced
the conversion products observed in C. Middle: In the presence
of 2 mM ATP, the conversion reaction was observed with the
MukBhd^EQ-containing complex, but not with the
MukBhd^SR-containing complex. Right: Conversion of the triple
complexes containing the indicated MukB head did not take place,
when incubated without ATP.
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Figure 7.
Figure 7. Heterogeneity, Head Domain Contacts and Opening of
the MukBEF Ring Structures
(A) Architectural heterogeneity.
Three examples of closed ring structures, including MukB–MukEF
are schematically drawn. The portion enclosed in the dotted box
is presented in ribbon drawing in the inset.
(B) Effect of
MukEF on contacts between MukB heads. The MukEF frame in
MukB–MukEF prohibits intracomplex head domain contact.
Diffusional, intercomplex-wise head domain contact should be
infrequent (left). The MukEF frame in a higher-order complex
restricts free diffusion of MukB heads and their contacts within
the complex can be frequent (right).
(C) Ring opening.
Opening of the closed ring structures via intercomplex and
intracomplex head domain engagement is illustrated. The arrows
indicate contacts for head domain engagement. The portion of the
two MukB–MukEF rings enclosed in the dotted box is presented
in ribbon drawing in the inset. One of the two rings (left) has
an opening between its MukB head and MukF C-WHD. The
architectures of MukB–MukEF in the insets in A and C were
constructed based on the presented structures.
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The above figures are
reprinted
by permission from Cell Press:
Cell
(2009,
136,
85-96)
copyright 2009.
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