Nicotinamide riboside kinase structures reveal new pathways to NAD+.

Wolfram Tempel,Anthony A Sauve,Tianle Yang,Wael M Rabeh,Hee-Won Park,Katrina L Bogan,Heather F Seidle,Marzena Wojcik,Lyudmila Nedyalkova,Peter Belenky,Charles Brenner

doi:10.1371/journal.pbio.0050263

Wolfram Tempel, Anthony A Sauve + Show 9 more

Open Access

https://doi.org/10.1371/journal.pbio.0050263

Copy DOI

Abstract

The eukaryotic nicotinamide riboside kinase (Nrk) pathway, which is induced in response to nerve damage and promotes replicative life span in yeast, converts nicotinamide riboside to nicotinamide adenine dinucleotide (NAD+) by phosphorylation and adenylylation. Crystal structures of human Nrk1 bound to nucleoside and nucleotide substrates and products revealed an enzyme structurally similar to Rossmann fold metabolite kinases and allowed the identification of active site residues, which were shown to be essential for human Nrk1 and Nrk2 activity in vivo. Although the structures account for the 500-fold discrimination between nicotinamide riboside and pyrimidine nucleosides, no enzyme feature was identified to recognize the distinctive carboxamide group of nicotinamide riboside. Indeed, nicotinic acid riboside is a specific substrate of human Nrk enzymes and is utilized in yeast in a novel biosynthetic pathway that depends on Nrk and NAD+ synthetase. Additionally, nicotinic acid riboside is utilized in vivo by Urh1, Pnp1, and Preiss-Handler salvage. Thus, crystal structures of Nrk1 led to the identification of new pathways to NAD+.

Highlights

NADþ functions both as a co-enzyme for hydride transfer reactions and as a substrate for NADþ-consuming enzymes including Sirtuins and poly(ADPribose) polymerases [1]
Biosynthesis of nicotinamide adenine dinucleotide (NADþ) is fundamental to cells, because NADþ is an essential co-factor for metabolic and gene regulatory pathways that control life and death
We recently discovered nicotinamide riboside (NR) as a third vitamin precursor of NADþ in eukaryotes, which extends yeast life span without caloric restriction and protects damaged dorsal root ganglion neurons from degeneration

Summary

Introduction

NADþ functions both as a co-enzyme for hydride transfer reactions and as a substrate for NADþ-consuming enzymes including Sirtuins and poly(ADPribose) polymerases [1]. NR, a natural product present in milk [4], increases NADþ biosynthesis, increases Sir2-dependent gene silencing, and extends yeast life span via two NR salvage pathways [15]. The first NR salvage pathway depends on NR phosphorylation by a specific kinase, encoded by the products of the yeast and human NRK1 genes or the human NRK2 gene [4]. The second NR salvage pathway is Nrk-independent and is initiated by the activity of yeast Urh, Pnp , and, to a slight degree, Meu, which split NR into a ribosyl product and Nam for resynthesis of NADþ via Nam salvage [15]. The second pathway of NR salvage has yet to be investigated in mammalian systems, Pnp and Meu are the yeast homologs of human purine nucleoside phosphorylase and methylthioadenosine phosphorylase, suggesting that human NR salvage may depend on Nrk, Nrk, and Pnp [15]

Methods

Results

Discussion

Conclusion