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PDBsum entry 2ipc
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Transport protein
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PDB id
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2ipc
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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 the translocation atpase seca from thermus thermophilus reveals a parallel, Head-To-Head dimer.
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Authors
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D.G.Vassylyev,
H.Mori,
M.N.Vassylyeva,
T.Tsukazaki,
Y.Kimura,
T.H.Tahirov,
K.Ito.
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Ref.
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J Mol Biol, 2006,
364,
248-258.
[DOI no: ]
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PubMed id
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Abstract
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The mechanism of pre-protein export through the bacterial cytoplasmic membrane,
in which the SecA ATPase plays a crucial role as an "energy supplier",
is poorly understood. In particular, biochemical and structural studies provide
contradictory data as to the oligomeric state of SecA when it is integrated into
the active trans-membrane translocase. Here, we report the 2.8 A resolution
crystal structure of the Thermus thermophilus SecA protein (TtSecA). Whereas the
structure of the TtSecA monomer closely resembles that from other bacteria, the
oligomeric state of TtSecA is strikingly distinct. In contrast to the
antiparallel (head-to-tail) dimerization reported previously for the other
bacterial systems, TtSecA forms parallel (head-to-head) dimers that are
reminiscent of open scissors. The dimer interface is abundant in bulky Arg and
Lys side-chains from both subunits, which stack on one another to form an
unusual "basic zipper" that is highly conserved, as revealed by
homology modeling and sequence analysis. The basic zipper is sealed on both ends
by two pairs of the salt bridges formed between the basic side-chains from the
zipper and two invariant acidic residues. The organization of the dimers, in
which the two pre-protein binding domains are located proximal to each other at
the tip of the "scissors", might allow a concerted mode of substrate
recognition while the opening/closing of the scissors might facilitate
translocation.
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Figure 1.
Figure 1. The TtSecA structure. (a) The ribbon diagram of
the parallel dimer. The two distinct views are shown. BH, the
bridge helix. (b) Superposition of the TtSecA and RNA polymerase
bridge helices.
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Figure 4.
Figure 4. Implications for translocation. (a) The surface
representation of the TtSecA dimer (gray) showing the cavity
formed between the PPXD and C-terminal domains exposing a large
number of the hydrophobic residues (yellow) that might
constitute a putative pre-protein (red ellipse) binding site.
(b) Sequence alignment showing conservation of the hydrophobic
residues (yellow boxes) in the cavity.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2006,
364,
248-258)
copyright 2006.
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