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PDBsum entry 1q43
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Transport protein
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PDB id
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1q43
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Contents |
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* Residue conservation analysis
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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 basis for modulation and agonist specificity of hcn pacemaker channels.
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Authors
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W.N.Zagotta,
N.B.Olivier,
K.D.Black,
E.C.Young,
R.Olson,
E.Gouaux.
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Ref.
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Nature, 2003,
425,
200-205.
[DOI no: ]
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PubMed id
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Abstract
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The family of hyperpolarization-activated, cyclic nucleotide-modulated (HCN)
channels are crucial for a range of electrical signalling, including cardiac and
neuronal pacemaker activity, setting resting membrane electrical properties and
dendritic integration. These nonselective cation channels, underlying the I(f),
I(h) and I(q) currents of heart and nerve cells, are activated by membrane
hyperpolarization and modulated by the binding of cyclic nucleotides such as
cAMP and cGMP. The cAMP-mediated enhancement of channel activity is largely
responsible for the increase in heart rate caused by beta-adrenergic agonists.
Here we have investigated the mechanism underlying this modulation by studying a
carboxy-terminal fragment of HCN2 containing the cyclic nucleotide-binding
domain (CNBD) and the C-linker region that connects the CNBD to the pore. X-ray
crystallographic structures of this C-terminal fragment bound to cAMP or cGMP,
together with equilibrium sedimentation analysis, identify a tetramerization
domain and the mechanism for cyclic nucleotide specificity, and suggest a model
for ligand-dependent channel modulation. On the basis of amino acid sequence
similarity to HCN channels, the cyclic nucleotide-gated, and eag- and
KAT1-related families of channels are probably related to HCN channels in
structure and mechanism.
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Figure 2.
Figure 2: Structure of the mouse HCN2 C-linker and CNBD
construct bound to cAMP. a, Ribbon representation of a single
protomer of HCN2J with cAMP. b, HCN2 tetramer viewed
perpendicular (left) and parallel (right) to the four-fold axis.
Each subunit is shown in a different colour. c, Molecular
surface representation of the tetramer, coloured according to
the calculated electrostatic potential and viewed parallel to
the four-fold axis from the intracellular side of the membrane
(right). Residues Glu 451, Asp 487, Asp 489 and Asp 609 protrude
toward the central axis of the tetramer. The view on the left is
perpendicular to the four-fold axis, and the molecule has been
sliced along the symmetry axis.
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Figure 4.
Figure 4: C-linker interactions and cyclic nucleotide-dependent
tetramer formation. a, Stereoview of intersubunit C-linker
contacts. Helices A' and B' of one protomer are in red, and
helices C' and D' of an adjacent protomer are in blue. b, HCN2I
sedimentation equilibrium data in the absence (top) and presence
(bottom) of cAMP. The measurements and the models used to fit
the experimental data are shown as open yellow circles and thin
black lines, respectively. The thick black, red and blue lines
represent, respectively, the proportion of monomer, dimer and
tetramer calculated from the models. The residuals are shown for
a monomer -dimer (red) or a monomer -dimer -tetramer (blue)
model (top), and for a monomer -dimer (red) or a monomer
-tetramer (blue) model (bottom). c, Cartoon of an unliganded
closed channel (left) and a liganded open channel (right).
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2003,
425,
200-205)
copyright 2003.
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