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PDBsum entry 1git
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Gtp-binding protein
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PDB id
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1git
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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 gdp-Pi complex of gly203-->Ala gialpha1: a mimic of the ternary product complex of galpha-Catalyzed gtp hydrolysis.
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Authors
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A.M.Berghuis,
E.Lee,
A.S.Raw,
A.G.Gilman,
S.R.Sprang.
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Ref.
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Structure, 1996,
4,
1277-1290.
[DOI no: ]
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PubMed id
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Note In the PDB file this reference is
annotated as "TO BE PUBLISHED".
The citation details given above were identified by an automated
search of PubMed on title and author
names, giving a
percentage match of
84%.
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Abstract
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BACKGROUND: G proteins play a vital role in transmembrane signalling events. In
their inactive form G proteins exist as heterotrimers consisting of an alpha
subunit, complexed with GDP and a dimer of betagamma subunits. Upon stimulation
by receptors, G protein alpha subunits exchange GDP for GTP and dissociate from
betagamma . Thus activated, alphasubunits stimulate or inhibit downstream
effectors. The duration of the activated state corresponds to the single
turnover rate of GTP hydrolysis, which is typically in the range of seconds. In
Gialpha1, the Gly203-->Ala mutation reduces the affinity of the substrate for
Mg2+, inhibits a key conformational step that occurs upon GTP binding and
consequently inhibits the release of betagamma subunits from the GTP complex.
The structure of the Gly203-->Ala mutant of Gialpha1 (G203AGialpha1) bound to
the slowly hydrolyzing analog of GTP (GTPgammaS) has been determined in order to
elucidate the structural changes that take place during hydrolysis. RESULTS: We
have determined the three dimensional structure of a Gly203-->Ala mutant of
Gialpha1 at 2.6 A resolution. Although crystals were grown in the presence of
GTPgammaS and Mg2+, the catalytic site contains a molecule of GDP and a
phosphate ion, but no Mg2+. The phosphate ion is bound to a site near that
occupied by the gamma-phosphate of GTPgammaS in the activated wild-type alpha
subunit. A region of the protein, termed the Switch II helix, twists and bends
to adopt a conformation that is radically different from that observed in other
Gialpha1 subunit complexes. CONCLUSIONS: Under the conditions of
crystallization, the Gly203-->Ala mutation appears to stabilize a conformation
that may be similar, although perhaps not identical, to the transient ternary
product complex of Gialpha1-catalyzed GTP hydrolysis. The rearrangement of the
Switch II helix avoids a potential steric conflict caused by the mutation.
However, it appears that dissociation of the gamma-phosphate from the
pentacoordinate intermediate also requires a conformational change in Switch II.
Thus, a conformational rearrangement of the Switch II helix may be required in
Galpha-catalyzed GTP hydrolysis.
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Figure 2.
Figure 2. Molecular architecture of G203AG[iα1]. (a) Helical
segments are shown as green ribbons and β strands as blue
arrows; secondary structural elements near the catalytic site
are labeled, GDP and Pi are shown as ball-and-stick models.
Switch regions (Sw) are labeled (I–IV) and ‘N’ and
‘C’ mark the locations of residues 34 and 343, respectively.
(b) A superposition of the Cα traces of the G[iα1] subunit
bound to GDP (blue), G[iα1]bound to GTPγS–Mg^2+ (red), and
the GDP–Pi complex of G203AG[iα1] (green). The Cα atoms of
residues 40–178 and 220–340 were used to generate the
superposition. Figure 2. Molecular architecture of
G203AG[iα1]. (a) Helical segments are shown as green ribbons
and β strands as blue arrows; secondary structural elements
near the catalytic site are labeled, GDP and Pi are shown as
ball-and-stick models. Switch regions (Sw) are labeled
(I–IV) and ‘N’ and ‘C’ mark the locations of residues
34 and 343, respectively. (b) A superposition of the Cα traces
of the G[iα1] subunit bound to GDP (blue), G[iα1]bound to
GTPγS–Mg^2+ (red), and the GDP–Pi complex of G203AG[iα1]
(green). The Cα atoms of residues 40–178 and 220–340 were
used to generate the superposition. (Figure was generated using
the program SETOR [[3]55].)
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Figure 8.
Figure 8. Conformational states along the reaction pathway (see
text). (a) G[iα1]–GTPγS–Mg^2+. (b) Structure of the
pentacoordinate intermediate modeled on the structure of the
G[iα1]–GDP–AlF[4]^−–Mg^2+ complex. (c)
G[iα1]–GDP–Pi complex modeled on the structure of
G203A–GDP–Pi. (d) G[iα1]–GDP. Color scheme is the same as
that used in Figure 3. Figure 8. Conformational states along
the reaction pathway (see text). (a) G[iα1]–GTPγS–Mg^2+.
(b) Structure of the pentacoordinate intermediate modeled on the
structure of the G[iα1]–GDP–AlF[4]^−–Mg^2+ complex. (c)
G[iα1]–GDP–Pi complex modeled on the structure of
G203A–GDP–Pi. (d) G[iα1]–GDP. Color scheme is the same as
that used in [3]Figure 3. (Figure was generated using the
program SETOR [[4]55].)
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The above figures are
reprinted
by permission from Cell Press:
Structure
(1996,
4,
1277-1290)
copyright 1996.
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Secondary reference #1
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Title
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Tertiary and quaternary structural changes in gi alpha 1 induced by gtp hydrolysis.
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Authors
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M.B.Mixon,
E.Lee,
D.E.Coleman,
A.M.Berghuis,
A.G.Gilman,
S.R.Sprang.
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Ref.
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Science, 1995,
270,
954-960.
[DOI no: ]
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PubMed id
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Secondary reference #2
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Title
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Crystallization and preliminary crystallographic studies of gi alpha 1 and mutants of gi alpha 1 in the gtp and gdp-Bound states.
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Authors
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D.E.Coleman,
E.Lee,
M.B.Mixon,
M.E.Linder,
A.M.Berghuis,
A.G.Gilman,
S.R.Sprang.
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Ref.
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J Mol Biol, 1994,
238,
630-634.
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PubMed id
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Secondary reference #3
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Title
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Structures of active conformations of gi alpha 1 and the mechanism of gtp hydrolysis.
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Authors
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D.E.Coleman,
A.M.Berghuis,
E.Lee,
M.E.Linder,
A.G.Gilman,
S.R.Sprang.
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Ref.
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Science, 1994,
265,
1405-1412.
[DOI no: ]
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PubMed id
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