Fig. 1

Establishing NMN⁺ Biosynthetic Routes in Escherichia coli. NMN⁺ is produced in a small amount through the DNA ligase reaction in the E. coli cell. Heterologous enzymes, shown in green, can introduce new routes to generate NMN⁺. E. coli endogenous genes and transport processes are shown in blue. Pathway 1 introduces an NMN⁺ synthase from Francisella tularensis to produce NMN⁺ from NaMN⁺. Pathway 2, NR salvage, produces NAD⁺ from NR. Pathway 3, NA salvage, produces NMN⁺ from NA. The NMN⁺ transporter PnuC* from Salmonella enterica, shown in orange, enabled transport of NMN⁺ into the cell. The endogenous pncC, was targeted for gene disruption to prevent NMN⁺ degradation. In the presence of NAD⁺, NadR inhibits transcription of the genes involved in de novo NAD⁺ biosynthesis, nicotinate salvage, and E. coli pnuC. NaMN⁺, nicotinic acid mononucleotide; NaAD⁺, nicotinic adenine dinucleotide; NAD⁺, nicotinamide adenine dinucleotide; NMN⁺, nicotinamide mononucleotide; NR, nicotinamide riboside; NadD, NaMN adenylyltransferase; NadR, NMN adenylyltransferase; NadE, NAD synthase; Ft NadE*, NMN synthase from Francisella tularensis; PncC, NMN amidohydrolase; NadV, nicotinamide phosphoribosyltransferase; Pnuc, nicotinamide riboside transporter; Pnuc*, a mutant PnuC enabling direct transport of NMN⁺ across the cell membrane