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PDBsum entry 2qtv
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Protein transport
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PDB id
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2qtv
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Contents |
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733 a.a.
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164 a.a.
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36 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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Insights into copii coat nucleation from the structure of sec23.Sar1 complexed with the active fragment of sec31.
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Authors
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X.Bi,
J.D.Mancias,
J.Goldberg.
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Ref.
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Dev Cell, 2007,
13,
635-645.
[DOI no: ]
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PubMed id
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Abstract
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The COPII vesicular coat forms on the endoplasmic reticulum from Sar1-GTP,
Sec23/24 and Sec13/31 protein subunits. Here, we define the interaction between
Sec23/24.Sar1 and Sec13/31, involving a 40 residue Sec31 fragment. In the
crystal structure of the ternary complex, Sec31 binds as an extended polypeptide
across a composite surface of the Sec23 and Sar1-GTP molecules, explaining the
stepwise character of Sec23/24.Sar1 and Sec13/31 recruitment to the membrane.
The Sec31 fragment stimulates GAP activity of Sec23/24, and a convergence of
Sec31 and Sec23 residues at the Sar1 GTPase active site explains how GTP
hydrolysis is triggered leading to COPII coat disassembly. The Sec31 active
fragment is accommodated in a binding groove supported in part by Sec23 residue
Phe380. Substitution of the corresponding residue F382L in human Sec23A causes
cranio-lenticulo-sutural dysplasia, and we suggest that this mutation disrupts
the nucleation of COPII coat proteins at endoplasmic reticulum exit sites.
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Figure 3.
Figure 3. Crystal Structure of Sec23•Sar1 Complexed with
the Active Fragment of Sec31
The ribbon representation is
shown with the membrane-distal surface of the complex facing
forward. Sec23 is orange and Sar1 is red. The Sec31 active
fragment is in five colors: the N-terminal element that
interacts solely with Sar1 (purple, residues 907–920); a short
element that interacts with both Sec23 and Sar1 residues at the
interface (white, residues 920–922); two elements that
interact with Sec23 (blue, residues 923–927; green, residues
935–942); and the intervening stretch that interacts loosely
with Sec23 (yellow, residues 928–934). The blue contour lines
show difference electron density calculated prior to the
inclusion of the Sec31 active fragment (at 2.5 Å
resolution, contoured at 2.9 σ). Domains of the Sec23 protein
are labeled, and the interface with Sec24 is indicated at the
bottom of the picture. The switch 2 (labeled Sw2) and helix α3
elements of Sar1 to which Sec31 binds are indicated.
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Figure 4.
Figure 4. Layered Appearance of COPII Coat Proteins in a
Model of Sec23/24•Sar1 Bound to Sec31
The ribbon
representation on the left is a side view of Sec23/24•Sar1
complexed with the Sec31 active fragment. Sec23 is orange, Sar1
is red, GppNHp is blue, the Sec31 fragment is blue, and Sec24 is
green. This is a composite model that includes Sec24 taken from
a Sec23/24 crystal structure determined previously (Bi et al.,
2002). The gray line indicates the curvature of membrane
vesicle, and the dotted red line suggests the attachment of Sar1
to membrane via its N-terminal sequence. The view on the right
is rotated 90° to show the membrane-distal surface in
space-filling representation (same orientation as in Figure 3).
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The above figures are
reprinted
from an Open Access publication published by Cell Press:
Dev Cell
(2007,
13,
635-645)
copyright 2007.
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