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PDBsum entry 1m2v
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Protein transport
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PDB id
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1m2v
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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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Structure of the sec23/24-Sar1 pre-Budding complex of the copii vesicle coat.
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Authors
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X.Bi,
R.A.Corpina,
J.Goldberg.
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Ref.
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Nature, 2002,
419,
271-277.
[DOI no: ]
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PubMed id
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Abstract
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COPII-coated vesicles form on the endoplasmic reticulum by the stepwise
recruitment of three cytosolic components: Sar1-GTP to initiate coat formation,
Sec23/24 heterodimer to select SNARE and cargo molecules, and Sec13/31 to induce
coat polymerization and membrane deformation. Crystallographic analysis of the
Saccharomyces cerevisiae Sec23/24-Sar1 complex reveals a bow-tie-shaped
structure, 15 nm long, with a membrane-proximal surface that is concave and
positively charged to conform to the size and acidic-phospholipid composition of
the COPII vesicle. Sec23 and Sar1 form a continuous surface stabilized by a
non-hydrolysable GTP analogue, and Sar1 has rearranged from the GDP conformation
to expose amino-terminal residues that will probably embed in the bilayer. The
GTPase-activating protein (GAP) activity of Sec23 involves an arginine side
chain inserted into the Sar1 active site. These observations establish the
structural basis for GTP-dependent recruitment of a vesicular coat complex, and
for uncoating through coat-controlled GTP hydrolysis.
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Figure 1.
Figure 1: Structure of the Sec23/24 -Sar1 pre-budding complex.
Ribbon representation is shown as successive 90° rotations.
Sec23 is yellow, Sec24 green and Sar1 red. a, Front view along
the dyad relating the coat subunits, with the membrane-proximal
surface facing forward. b, Side view. The grey line indicates
the curvature of a 60-nm COPII vesicle, drawn to scale. c, Top
view. The three regions of Sar1 that would face the membrane are
labelled C, N and  2
- 3.
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Figure 3.
Figure 3: Surface features of the Sec23/24 complex a, Molecular
surface coloured according to electrostatic potential50:
negative potential is red and positive potential blue. Sar1
is drawn as a backbone tube in magenta. The three views are
successive 90° rotations around a vertical axis. In the left
image, the membrane-proximal surface faces forwards. b, Surface
of Sec23/24 coloured according to sequence conservation of the
underlying residues in an alignment of Sec23 sequences from six
organisms (human Sec23A, Drosophila melanogaster, Neurospora
crassa, Schizosaccharomyces pombe, Arabidopsis thaliana and
Saccharomyces cerevisiae) and Sec24 sequences from four
organisms (human Sec24A, S. pombe, A. thaliana and S.
cerevisiae). Labels I, II and III indicate three highly
conserved patches (see text for details). The orientations are
the same as in a, with Sar1 omitted.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2002,
419,
271-277)
copyright 2002.
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