Nicotinamide riboside kinase structures reveal new pathways to NAD+.
Nicotinamide riboside kinase structures reveal new pathways to NAD+.
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DOI：
10.1371/journal.pbio.0050263
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发表时间：
2007-10-02
期刊：
影响因子：
9.8
通讯作者：
Brenner, Charles
中科院分区：
文献类型：
--
作者：
Tempel, Wolfram;Rabeh, Wael M;Bogan, Katrina L;Belenky, Peter;Wojcik, Marzena;Seidle, Heather F;Nedyalkova, Lyudmila;Yang, Tianle;Sauve, Anthony A;Park, Hee-Won;Brenner, Charles
真核细胞中的烟酰胺核苷激酶(NRK)通路是在酵母中诱导神经损伤并延长复制寿命的途径，通过磷酸化和腺苷化将烟酰胺核苷转化为烟酰胺腺嘌呤二核苷酸(NAD+)。与核苷、核苷酸底物和产物结合的人Nrk1的晶体结构揭示了一种结构上类似于Rossmann折叠代谢物激酶的酶，并允许鉴定活性部位残基，这被证明是人体Nrk1和NRK2活性所必需的。虽然这些结构解释了烟酰胺核苷和嘧啶核苷之间500倍的区别，但没有鉴定出识别烟酰胺核苷独特的羧胺基团的酶特性。事实上，烟酸核苷是人类NRK酶的特定底物，在酵母中被用于依赖NRK和NAD+合成酶的一种新的生物合成途径。此外，烟酸核苷在体内被Urh1、Pnp1和Preiss-Handler回收利用。因此，Nrk1的晶体结构导致了NAD+的新途径的确定。烟酰胺腺嘌呤二核苷酸(NAD+)的生物合成是细胞的基础，因为NAD+是控制生死的代谢和基因调控途径的重要辅助因子。1938年发现了NAD+的两种维生素前体。我们最近发现烟酰胺核苷(NR)是真核生物中NAD+的第三种维生素前体，它可以延长酵母的寿命而不限制热量，并保护受损的背根节神经元免受退化。从NR生物合成NAD+需要两个途径中的任何一个的酶活性。在一种途径中，包括人类NRK1和NRK2在内的特定NR激酶将NR磷酸化为烟酰胺单核苷酸。第二个不依赖于NRK的途径是由酵母核苷裂解酶UHH1和Pnp1启动的。我们解析了人Nrk1的五种晶体结构，并根据与底物的共晶结构，表明该酶可能能够磷酸化一种新的化合物--烟酸核苷(NAR)。然后，我们在体外证明了人NRK酶具有NR/NAR激酶的双重特异性，并且我们在活的酵母细胞中通过Nrk1、URh1和Pnp1启动的途径建立了NAR作为NAD+的维生素前体的能力。因此，从人类Nrk1的结构出发，我们发现了NAD+的合成维生素前体，提示NAR可能是正常的NAD+代谢物。真核生物烟酰胺核苷激酶(NRK)通过磷酸化和腺苷化将烟酰胺核苷转化为NAD+。这种酶与几种底物结合的结构导致了NAD+的新途径的鉴定
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+. Biosynthesis of nicotinamide adenine dinucleotide (NAD+) is fundamental to cells, because NAD+ is an essential co-factor for metabolic and gene regulatory pathways that control life and death. Two vitamin precursors of NAD+ were discovered in 1938. We recently discovered nicotinamide riboside (NR) as a third vitamin precursor of NAD+ in eukaryotes, which extends yeast life span without caloric restriction and protects damaged dorsal root ganglion neurons from degeneration. Biosynthesis of NAD+ from NR requires enzyme activities in either of two pathways. In one pathway, specific NR kinases, including human Nrk1 and Nrk2, phosphorylate NR to nicotinamide mononucleotide. A second and Nrk-independent pathway is initiated by yeast nucleoside-splitting enzymes, Urh1 and Pnp1. We solved five crystal structures of human Nrk1 and, on the basis of co-crystal structures with substrates, suggested that the enzyme might be able to phosphorylate a novel compound, nicotinic acid riboside (NaR). We then demonstrated that human Nrk enzymes have dual specificity as NR/NaR kinases in vitro, and we established the ability of NaR to be used as a vitamin precursor of NAD+ via pathways initiated by Nrk1, Urh1, and Pnp1 in living yeast cells. Thus, starting from the structure of human Nrk1, we discovered a synthetic vitamin precursor of NAD+ and suggest the possibility that NaR is a normal NAD+ metabolite. Eukaryotic nicotinamide riboside kinase (Nrk) converts nicotinamide riboside to NAD+ by phosphorylation and adenylylation. The structures of this enzyme bound to several substrates lead to identification of new pathways to NAD+