Flavin Mononucleotide

Using a structure‑based drug design strategy targeting the FMN riboswitch, the authors developed the fluoro‑phenyl derivative 5FDQD, which protects mice against Clostridium difficile. The approach integrated structural analysis of FMN riboswitch, derivative synthesis, chemical probing for binding, in vitro transcription termination assays, and crystal structures of the riboswitch with mature candidates. The work delineates principles for productive riboswitch binding and demonstrates the effectiveness of a coordinated structure‑guided approach to designing RNA‑targeting antibiotics.

Fig. 1 Roseoflavin mononucleotide at the center of a medicinal chemistry optimization strategy that led to the discovery of synthetic analogs with potent activity and selectivity. (Vicens Q, et al., 2018)

Using Aspergillus niger Fdc1 as a model, the study shows that isomerization of the prFMN^iminium^ cofactor to prFMN^ketimine^ is light‑dependent, irreversible, and leads to loss of activity, independent of the conserved Glu‑Arg‑Glu network. In contrast, catalysis and oxidative maturation to form prFMN^iminium^ depend on an intact Glu‑Arg‑Glu network; only Glu→Asp substitutions retain activity. The R173A variant severely impairs oxidative maturation. The network plays distinct roles in catalysis versus cofactor isomerization.

Fig. 2 Overview of prFMN maturation and catalysis in Fdc1. (Bailey SS, et al., 2018)