Identification of evolutionary and kinetic drivers of NAD-dependent signaling

NAD provides an important link between metabolism and signal transduction and has emerged as centralhub between bioenergetics and all major cellular events. NAD-dependent signalling, e.g. by sirtuins andPARPs, consumes considerable amounts of NAD. To maintain physiological functions, NAD consumptionand biosynthesis need to be carefully balanced. Using extensive phylogenetic analyses, mathematicalmodelling of NAD metabolism and experimental verification, we show that the diversification of NADdependent signalling in vertebrates depended on three critical evolutionary events: i) the transition of NADbiosynthesis to exclusive usage of nicotinamide phosphoribosyltransferase (NamPT); ii) the occurrence ofnicotinamide N-methyltransferase (NNMT), which diverts nicotinamide (Nam) from recycling into NAD,preventing Nam accumulation and inhibition of NAD-dependent signalling reactions and iii) structuraladaptation of NamPT, providing an unusually high affinity towards Nam, necessary to maintain NADlevels. Our results reveal an unexpected co-evolution and kinetic interplay between NNMT and NamPTthat enables extensive NAD signalling. This has implications for therapeutic strategies of NADsupplementation and the use of NNMT or NamPT inhibitors in disease treatment