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![[Figure 8]](rr5135fig8mag.jpg)
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Figure 8
Comparison of the active and allosteric sites. (a) The active site in protomer B of hlFBPase is shown as a surface. The σA-weighted OMIT electron-density map contoured at 4 r.m.s.d. of the sulfate ions is drawn as a green mesh. The black mesh is a Fourier map using anomalous differences and refined phases as coefficients contoured at 7 r.m.s.d. The Zn2+ ion (black sphere) is coordinated by four acidic side chains and a water molecule in trigonal bipyramidal geometry. The transparent blue plane shows the base of the bipyramid. Possible hydrogen bonds (<3.2 Å) are shown as blue dashed lines. In the absence of a carbohydrate, a chain of water molecules (red spheres) fills the active site. (b) Active site of porcine FBPase in complex with F6P and phosphate (PDB entry 1cnq). The location of the sufate ions in hlFBPase is close, but not identical, to the phosphates in this product complex. Three Zn2+ ions (small black spheres) were found in this structure. In general, the metal sites are denoted M1–M3. A notable difference from the hlFBPase structure is a Lys274 side chain that binds to the O4′ atom of F6P but is flipped away in the apo state of hlFBPase. Asp68 is contributed from the catalytic loop, which has closed onto the active site of FBPase, but is disordered in hlFBPase. (c) Active site of porcine FBPase in complex with the competitive inhibitor F-2,6-P2 (PDB entry 2qvv). The 2′-phosphoryl group is located halfway between the positions of the inorganic phosphate in the product complex (b) and the sulfate ion in apo hlFBPase (a). The coordination of the Zn2+ ion is trigonal bipyramidal, but in a different arrangement compared with hlFBPase. The transparent blue plane shows the base of the bipyramid. (d) Allosteric AMP site in hlFBPase. A loop region is disordered and marked by grey spheres. The red mesh is the σA-weighted OMIT electron-density map contoured at 4 r.m.s.d. around the sulfate ion, which is bound to the phosphate-binding loop (P-loop) and the N-terminus of an α-helix. (e) The allosteric AMP site in porcine FBPase in complex with AMP. The loop that is missing in the hlFBPase structure is ordered in this complex. The sulfate ion in hlFBPase binds at the same position as the phosphoryl moiety of AMP. (f) Allosteric AMP site in porcine FBPase in complex with sulfate (PDB entry 2qvv). The hydrogen-bonding pattern is the same as in hlFBPase shown in (d). |
![[Figure 8]](rr5135fig8.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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