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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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