 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 2]](hv5090fig2mag.jpg)
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Figure 2
(a) Fluorescence titration of the aminothiazole ligand against E. coli KAS I protein. The protein concentration was 4.9 µM in binding-assay buffer (20 mM Tris pH 7.5, 200 mM NaCl, 1 mM TCEP, 0.5 mM EDTA). The excitation and emission wavelengths were 280 and 340 nm, respectively. Owing to the high absorption coefficient of the compound at 340 nm, the efficient dipole–dipole interaction strongly quenched the emission of both tryptophan residues of the protein. Circles show the fluorescence intensity in arbitrary units after correction for filter effects; the line shows a sigmoidal fit resulting in an equilibrium dissociation constant Kd of 25 µM. (b) Sedimentation equilibrium of the aminothiazole compound in the absence and presence of E. coli KAS I. The absorbance profiles were recorded at 16 000 rev min−1 at 380 nm for 100 µM aminothiazole in the absence or presence of 22.7 µM E. coli KAS I. At this wavelength the absorbance of the protein is negligible, so that only the ligand was detected. The ligand alone showed a flat radial profile for this rotational speed (triangles). In the presence of E. coli KAS I the radial concentration profile corresponds to the protein molar mass, demonstrating binding of the ligand (circles). |
![[Figure 2]](hv5090fig2.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
