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![[Figure 4]](gm5115fig4mag.jpg)
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Figure 4
Natural ligands in FABPs that could not be replaced by other molecules. Stereochemical incompatibilities are annotated by red dashed lines. Possible hydrogen bonds are shown by black and green dashed lines, where black indicates hydrogen-bond contacts that were present in the original structure and green indicates newly formed hydrogen bonds after replacement of the ligand with a fatty acid. Atoms of the ligand that were set to zero occupancy in the original structures are shown as spheres. 2Fo − Fc electron densities are contoured at 0.8 r.m.s.d. (a) The hypoglycemic agent troglitazone was built into the U-shaped electron density of an endogenous fatty acid bound to mouse FABP4 (PDB entry 2qm9). About half of the ligand was set to zero occupancy. The ligand has an unusual conformation and its hydrophobic parts clash with the polar residues that normally bind the carboxylate group. Myristate (bottom) or a longer fatty acid refines well at this position, has no clashes and engages in productive hydrogen bonds (green dashes). (b) Cholesterol was assumed to bind to human FABP7 but is also in stereochemical conflict with the protein surroundings (PDB entry 8ivl). Three atoms within cholesterol that are located outside the observed electron density were set to zero occupancy. Again, myristate or a longer fatty acid refines well at this position. Re-refined models in complex with fatty acids and structure factors are available in the supporting information. |
![[Figure 4]](gm5115fig4.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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