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PDBsum entry 2qa5
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Cell cycle, structural protein
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PDB id
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2qa5
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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 insight into filament formation by mammalian septins.
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Authors
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M.Sirajuddin,
M.Farkasovsky,
F.Hauer,
D.Kühlmann,
I.G.Macara,
M.Weyand,
H.Stark,
A.Wittinghofer.
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Ref.
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Nature, 2007,
449,
311-315.
[DOI no: ]
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PubMed id
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Abstract
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Septins are GTP-binding proteins that assemble into homo- and hetero-oligomers
and filaments. Although they have key roles in various cellular processes,
little is known concerning the structure of septin subunits or the organization
and polarity of septin complexes. Here we present the structures of the human
SEPT2 G domain and the heterotrimeric human SEPT2-SEPT6-SEPT7 complex. The
structures reveal a universal bipolar polymer building block, composed of an
extended G domain, which forms oligomers and filaments by conserved interactions
between adjacent nucleotide-binding sites and/or the amino- and carboxy-terminal
extensions. Unexpectedly, X-ray crystallography and electron microscopy showed
that the predicted coiled coils are not involved in or required for complex
and/or filament formation. The asymmetrical heterotrimers associate head-to-head
to form a hexameric unit that is nonpolarized along the filament axis but is
rotationally asymmetrical. The architecture of septin filaments differs
fundamentally from that of other cytoskeletal structures.
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Figure 2.
Figure 2: Structural analysis of the human septin complex. a,
Superimposition of the molecular replacement solution using the
SEPT2 G domain onto the selenomethionine anomalous map contoured
at 5  to
assign the location of the SEPT2, SEPT6 and SEPT7 subunits in
the asymmetrical unit. b, Ribbon model of the trimeric
SEPT2–SEPT26–SEPT27 complex, with SEPT7 in cyan, SEPT6 in
pink and SEPT2 in blue, with nucleotides in ball and stick
representation. c, Positive F[o] - F[c] electron density map,
contoured at 3 ,
around the nucleotide-binding sites of the respective septins,
and the resulting nucleotide models, as indicated.
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Figure 4.
Figure 4: The septin filament. Surface representation of
the basic hexameric unit (in colour). The neighbouring hexamer
makes longitudinal contact using SEPT7 (in grey), thereby
forming septin filaments. The nature of the nucleotide in the
subunits is indicated. The presumed orientations of the
C-terminal ends predicted to form coiled coils are shown
schematically.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2007,
449,
311-315)
copyright 2007.
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