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PDBsum entry 1rv8
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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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Induced fit movements and metal cofactor selectivity of class ii aldolases: structure of thermus aquaticus fructose-1,6-Bisphosphate aldolase.
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Authors
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T.Izard,
J.Sygusch.
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Ref.
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J Biol Chem, 2004,
279,
11825-11833.
[DOI no: ]
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PubMed id
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Abstract
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Fructose-1,6-bisphosphate (FBP) aldolase is an essential glycolytic enzyme that
reversibly cleaves its ketohexose substrate into triose phosphates. Here we
report the crystal structure of a metallo-dependent or class II FBP aldolase
from an extreme thermophile, Thermus aquaticus (Taq). The quaternary structure
reveals a tetramer composed of two dimers related by a 2-fold axis. Taq FBP
aldolase subunits exhibit two distinct conformational states corresponding to
loop regions that are in either open or closed position with respect to the
active site. Loop closure remodels the disposition of chelating active site
histidine residues. In subunits corresponding to the open conformation, the
metal cofactor, Co(2+), is sequestered in the active site, whereas for subunits
in the closed conformation, the metal cation exchanges between two mutually
exclusive binding loci, corresponding to a site at the active site surface and
an interior site vicinal to the metal-binding site in the open conformation.
Cofactor site exchange is mediated by rotations of the chelating histidine side
chains that are coupled to the prior conformational change of loop closure.
Sulfate anions are consistent with the location of the phosphate-binding sites
of the FBP substrate and determine not only the previously unknown second
phosphate-binding site but also provide a mechanism that regulates loop closure
during catalysis. Modeling of FBP substrate into the active site is consistent
with binding by the acyclic keto form, a minor solution species, and with the
metal cofactor mediating keto bond polarization. The Taq FBP aldolase structure
suggests a structural basis for different metal cofactor specificity than in
Escherichia coli FBP aldolase structures, and we discuss its potential role
during catalysis. Comparison with the E. coli structure also indicates a
structural basis for thermostability by Taq FBP aldolase.
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Figure 2.
FIG. 2. A cartoon drawing of the FBP aldolase oligomer with
point group 222. The three different molecular dyads comprise a
right-handed orthogonal set of axes P, Q, and R as originally
defined for the three 2-fold axes of lactate dehydrogenase (46).
In A, the view is looking down the crystallographic dyad (P),
while in B the orientation is looking down the molecular dyad
(R). The dyads (R and Q in A and P and Q in B) are indicated by
solid lines. Each protomer is shown in a different color.
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Figure 4.
FIG. 4. Stereo view of Taq FBP aldolase active site. Final
 [A]
weighted F[o] - F[c] omit electron density map for ligands bound
to the enzyme. The contour level of the electron density map is
4 ,
and the resolution is 2.3 Å. The bonds of the ligands are
drawn in pink, whereas the bonds of the enzyme are shown in
light gray. For clarity, water molecules (drawn as spheres) are
not labeled. Residues belonging to a 2-fold related subunit are
italicized. A, protomer in the closed conformation showing
residues in contact with the sulfate anions that coincide with
the phosphate-binding sites of FBP, the two mutually exclusive
Co2+ cofactors (drawn as light blue spheres) and the activating
cation (drawn as a black sphere). B, sulfate and cation binding
to the active site as observed in the subunits in their open
conformation. Orientation was rotated by 15° with respect to
A to reveal Asn251 that interacts with the monovalent cation. C,
FBP modeled into the active site using the sulfate-binding sites
of the closed protomer as phosphate oxyanion templates in the
Taq FBP aldolase complex with yttrium. The novel metal-binding
site (yttrium) is drawn as a green sphere. The hydroxyls O[2]
and O[3] of the FBP molecule are within close contact of the
exterior Co2+ site (indicated by dashed lines).
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
11825-11833)
copyright 2004.
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