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PDBsum entry 2j1d
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Protein binding
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PDB id
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2j1d
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References listed in PDB file
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Key reference
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Title
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Structure of the fh2 domain of daam1: implications for formin regulation of actin assembly.
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Authors
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J.Lu,
W.Meng,
F.Poy,
S.Maiti,
B.L.Goode,
M.J.Eck.
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Ref.
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J Mol Biol, 2007,
369,
1258-1269.
[DOI no: ]
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PubMed id
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Note In the PDB file this reference is
annotated as "TO BE PUBLISHED".
The citation details given above were identified by an automated
search of PubMed on title and author
names, giving a
perfect match.
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Abstract
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Daam1 (dishevelled-associated activator of morphogenesis-1) is a
diaphanous-related formin first studied as a novel dishevelled binding protein
and shown to be crucial for the planar cell polarity (PCP) pathway in Xenopus.
Daam1, like other formins, directs nucleation and elongation of new actin
filaments using its conserved formin-homology-2 (FH2) domain. Here we report the
crystal structure of a large C-terminal fragment of human Daam1 containing the
FH2 domain. The structure, determined at 2.25 A resolution using the
single-wavelength anomalous diffraction (SAD) phasing method, reveals a
"tethered dimer" architecture that is similar to that previously
described for the FH2 domain of the yeast formin Bni1, which shares
approximately 21% sequence identity with Daam1. Despite the overall similarity
with the dimeric FH2 domain of Bni1 and with a truncated monomeric structure of
mDia1, the Daam1 FH2 structure reveals a number of differences in secondary
structure elements and in the "lasso/post" dimerization interface that
may be functionally important. Most strikingly, the two halves of the
crystallographic dimer pack together in a manner that occludes their actin
binding surfaces. This "locked" conformation is stabilized by two
novel, interacting beta-strands formed by the ends of the linkers that connect
the two sides of the dimer. The Daam1 FH2 domain has weak actin assembly
activity as compared with other mammalian formins, but mutations that disrupt
the beta-strand lock increase activity about tenfold to a level comparable to
other formins, suggesting that this occluded conformation may represent an
auto-inhibited conformation of the Daam1 FH2 domain.
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Figure 1.
Figure 1. Crystal structure of the Daam1 FH2 domain. (a) The
domain structure of human Daam1. (b) Ribbon diagram showing the
overall structure of Daam1 FH2 domain. Sub-domains including the
lasso, the knob, the coiled-coil and the post region are
labeled. The invisible linker region is drawn manually with a
broken line for the purpose of illustration. The molecule is
colored using the visible spectrum (from blue at the N terminus
to red at the C terminus). (c) Ribbon diagram of the structure
of Daam1 FH2 dimer. The broken line separates the two
hemidimers. One molecule is colored the same way as in (b),
while the other is colored tan. (d) Sequence alignment and
secondary structure of the FH2 and DAD domains. Aligned
sequences are from human Daam1, murine Daam1, human Daam2,
murine Daam2, murine Dia1 and yeast (Saccharomyces cerevisiae)
Bni1p. Secondary structure elements are shown above the
sequences, with rectangles representing helices and thin lines
indicating non-helical regions. Conserved residues are colored
red. Figures were prepared using the program PyMoL [Delano,
W.L., The PyMol Molecular Graphics System (2002)
http://www.pymol.org].
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Figure 4.
Figure 4. Insights into interactions with actin via
comparisons with the structure of the Bni1/actin complex. (a)
and (b) The Daam1 FH2 structure is superimposed on the
Bni1/actin complex (PDB ID, 1Y64) in the regions of the knob
actin-binding site (a) and the lasso/post binding site (b). The
actin is colored blue, Daam1 magenta and Bni1 green. Selected
residues that are known to be important for actin assembly by
Bni1 are shown in stick form and labeled. (c) Overall views of
the Daam1 FH2 domain (magenta) superimposed on the Bni1/actin
complex (1Y64). Two actin subunits (yellow and orange) and two
Bni1 FH2 domains (green) from the Bni1/actin structure are
shown; this configuration may represent a “strained”
intermediate in FH2-mediated assembly or actin filaments.^29 The
side-chains of key actin binding residues are shown in CPK form
and are colored red (Ile698 and Lys847 in Daam1; Ile1431 and
Lys1601 in Bni1). The superposition was carried out using the
knob sub-domain only. Note that while the knob and post sites
independently superimpose well on the actin complex ((a) and
(b)), both cannot be simultaneously brought into register with
actin due to a different relative orientation of the knob
sub-domain. Bringing the knob into register (side view) leaves
the actin binding residues in the lasso/post region displaced
from actin by  vert,
similar 17 Å (best seen in the top view).
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The above figures are
reprinted
from an Open Access publication published by Elsevier:
J Mol Biol
(2007,
369,
1258-1269)
copyright 2007.
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