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PDBsum entry 2b5f
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Transport protein,membrane protein
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PDB id
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2b5f
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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 mechanism of plant aquaporin gating.
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Authors
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S.Törnroth-Horsefield,
Y.Wang,
K.Hedfalk,
U.Johanson,
M.Karlsson,
E.Tajkhorshid,
R.Neutze,
P.Kjellbom.
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Ref.
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Nature, 2006,
439,
688-694.
[DOI no: ]
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PubMed id
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Abstract
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Plants counteract fluctuations in water supply by regulating all aquaporins in
the cell plasma membrane. Channel closure results either from the
dephosphorylation of two conserved serine residues under conditions of drought
stress, or from the protonation of a conserved histidine residue following a
drop in cytoplasmic pH due to anoxia during flooding. Here we report the X-ray
structure of the spinach plasma membrane aquaporin SoPIP2;1 in its closed
conformation at 2.1 A resolution and in its open conformation at 3.9 A
resolution, and molecular dynamics simulations of the initial events governing
gating. In the closed conformation loop D caps the channel from the cytoplasm
and thereby occludes the pore. In the open conformation loop D is displaced up
to 16 A and this movement opens a hydrophobic gate blocking the channel entrance
from the cytoplasm. These results reveal a molecular gating mechanism which
appears conserved throughout all plant plasma membrane aquaporins.
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Figure 2.
Figure 2: Structures of the closed and open conformations of
SoPIP2;1. a, Stereo models of SoPIP2;1 in its open (blue) and
closed (green) conformations overlaid on that of AQP0 (light
grey; Protein Data Bank (PDB) entry 1YMG) and AQP1 (grey; PDB
entry 1J4N). b, c, Electron density for loop D in the closed (b)
and open (c) conformations. The structural model of the closed
conformation is coloured green and the open conformation is
coloured blue. Both 2F[o] - F[c] electron density maps are
contoured at 1.0  .
Residual electron density in c indicates that the closed
conformation is also present in partial occupancy.
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Figure 5.
Figure 5: Electron density at the sites of regulation by
phosphorylation and pH for SoPIP2;1 in its closed conformation.
a, Close-up view of the divalent-cation-binding site showing
the location of the Cd^2+ ion (purple) and the network of
hydrogen bonds linking Gly 30 and Glu 31 through Arg 118 to Arg
190 and Asp 191 of loop D. b, Close-up view of the
phosphorylation residue Ser 115, illustrating its hydrogen bond
to Glu 31. c, Electron density for Ser 274, which contacts Pro
199 and Leu 200 of a neighbouring monomer of the SoPIP2;1
tetramer. Overlaid in grey is the structure of the open
conformation of SoPIP2;1, indicating that a steric clash with
Leu 197 prevents helix 5 from adopting this conformation when
Ser 274 is dephosphorylated. d, Close-up view of His 193. When
protonated, an alternative conformation for His 193 (grey) may
be adopted that forms a salt bridge to Asp 28. All 2F[o] - F[c]
maps are contoured at 1.0 .
Numbers are distances in Å.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2006,
439,
688-694)
copyright 2006.
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