Extended Data Fig. 4: Effect of the concentration of 4 on formation of iminium 7 in SdnG and the H72A variant.
SdnG or its mutational variants (5 µM) were mixed with varied amounts of 4 and the mixture was immediately treated with 20 mM NaBH4. The reaction was subsequently analyzed by UHPLC-HRMS and the deconvoluted ESI-MS spectra were shown in the figure. Increased concentration of 4 promotes imine formation of SdnG but not the H72A variant. The result suggests that ligand binding is rate-determining for iminium formation in SdnG but not in the H72A variant. Therefore, diminished iminium formation in H72A is not a result of compromised ligand binding.
