Investigation of the binding of epimer A of the covalent hydrate of 6,7-bis(trifluoromethyl)-8-D-ribityllumazine to a recombinant F22W Bacillus subtilis lumazine synthase mutant by (15)N[(19)F] REDOR NMR.

The two epimeric covalent hydrates A and B of 6,7-bis(trifluoromethyl)-8-D-ribityllumazine are metabolically stable analogues of hypothetical intermediates proposed in the reactions catalyzed by riboflavin synthase and lumazine synthase. To confirm the stereochemical assignments previously based solely on results for epimer B, a (15)N[(19)F] REDOR NMR study was performed on the complex formed from epimer A and a recombinant, uniformly (15)N-labeled F22W mutant of Bacillus subtilis lumazine synthase. The results indicate that the fluorines of the ligands are closer to the side chain nitrogens of Arg127 and farther away from the side chain nitrogens of Lys135 in epimer B than in epimer A. These results are consistent with the assignment of the earlier 7R configuration of epimer A and the 7S configuration of epimer B.