Fig. 4
From: A revised biosynthetic pathway for the cofactor F420 in prokaryotes
Mtb-FbiB catalyzes reduction of dehydro-F420-0. a F420-1 is produced in FbiD:FbiA:FbiB coupled assays in the presence of Fre/FMNH2 and l-glutamate. Tandem mass spectrometry (MS/MS) confirmation of F420-1 in both negative (643.12811, [M − H]−) and positive (645.27094, [M + H]+) modes. b Mtb-FbiB is a bifunctional enzyme catalyzing the reduction of dehydro-F420-0 and its poly-glutamylation to form F420-n. c Docking of FMNH2 and dehydro-F420-0 into the crystal structure of FbiB C-terminal domain. The methylene group of the enolpyruvyl moiety sits in a pocket made up of M372 and P289, while the carboxylate hydrogen bonds with R337. The methylene double bond sits planar above the isoalloxazine ring of FMNH2 at an appropriate distance (3.6 Å, shown by dashed line) and oriented for a hydride transfer to the Si face of the methylene bond, accounting for the observed (S)-lactyl moiety of F420
