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PDBsum entry 3efd
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Immune system
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PDB id
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3efd
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Contents |
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211 a.a.
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215 a.a.
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30 a.a.
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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 full-Length kcsa in its closed conformation.
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Authors
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S.Uysal,
V.Vásquez,
V.Tereshko,
K.Esaki,
F.A.Fellouse,
S.S.Sidhu,
S.Koide,
E.Perozo,
A.Kossiakoff.
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Ref.
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Proc Natl Acad Sci U S A, 2009,
106,
6644-6649.
[DOI no: ]
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PubMed id
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Abstract
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KcsA is a proton-activated, voltage-modulated K(+) channel that has served as
the archetype pore domain in the Kv channel superfamily. Here, we have used
synthetic antigen-binding fragments (Fabs) as crystallographic chaperones to
determine the structure of full-length KcsA at 3.8 A, as well as that of its
isolated C-terminal domain at 2.6 A. The structure of the full-length KcsA-Fab
complex reveals a well-defined, 4-helix bundle that projects approximately 70 A
toward the cytoplasm. This bundle promotes a approximately 15 degree bending in
the inner bundle gate, tightening its diameter and shifting the narrowest point
2 turns of helix below. Functional analysis of the full-length KcsA-Fab complex
suggests that the C-terminal bundle remains whole during gating. We suggest that
this structure likely represents the physiologically relevant closed
conformation of KcsA.
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Figure 1.
Crystal structure of FL KcsA in complex with Fab2. (A) CDR
sequences of the 3 Fabs selected against FL KcsA from a
“reduced genetic code” phage display library. Numbering is
according to the Kabat definition (36). Gly is green; Tyr,
yellow, Ser, red; and nondiversified positions, gray. (B)
Crystal packing of the KcsA–Fab2 complex at 3.8 Å. KcsA
is in orange, and the light and heavy chains of the Fab are in
cyan (light chain) and magenta (heavy chain). (C) Simulated
annealing composite-omit 2Fo-Fc map (contoured at 1σ) of FL
KcsA. The red trace shows the fitted model as Cα tracing. (D)
The final model of the KcsA–Fab complex. Three regions
distinguished by the level of symmetry are highlighted: the
fourfold TM segments (blue color; residues 22–117), the
twofold bulge helix (red color; residues 118–135), and the
fourfold distal C-terminal bundle (gray color; residues
136–158). (E and F) Experimental (E) EPR mobility and (F)
NiEdda accessibility parameters (11) from membrane-reconstituted
FL KcsA, mapped on the crystal model of FL KcsA. The scales
represent a linear increase in local dynamics (E) and
accessibility to the aqueous media (F).
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Figure 2.
Influence of the C-terminal truncation on the conformation of
the inner helix bundle gate. (A) Cα superposition of the
high-resolution truncated KcsA structure (1K4C; red ribbons)
with FL KcsA (blue ribbons). Inset highlights the splaying out
of the inner helix bundle gate between residues 110 and 115,
resulting in a 15° outward tilting. (B) Radius profile
(calculated with the program HOLE; ref. 29) of truncated (red)
and FL KcsA (blue).
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