PDF(Pubmed)
Abstract：
The URH1p enzyme from the yeast Saccharomyces cerevisiae has gained significant interest due to its role in nitrogenous base metabolism, particularly involving uracil and nicotinamide salvage. Indeed, URH1p was initially classified as a nucleoside hydrolase (NH) with a pronounced preference for uridine substrate but was later shown to also participate in a Preiss-Handler-dependent pathway for recycling of both endogenous and exogenous nicotinamide riboside (NR) towards NAD+ synthesis. Here, we present the detailed enzymatic and structural characterisation of the yeast URH1p enzyme, a member of the group I NH family of enzymes. We show that the URH1p has similar catalytic efficiencies for hydrolysis of NR and uridine, advocating a dual role of the enzyme in both NAD+ synthesis and nucleobase salvage. We demonstrate that URH1p has a monomeric structure that is unprecedented for members of the NH homology group I, showing that oligomerisation is not strictly required for the N-ribosidic activity in this family of enzymes. The size, thermal stability and activity of URH1p towards the synthetic substrate 5-fluoruridine, a riboside precursor of the antitumoral drug 5-fluorouracil, make the enzyme an attractive tool to be employed in gene-directed enzyme-prodrug activation therapy against solid tumours.
摘要：
由于其在含氮碱基代谢中的作用，来自酿酒酵母的URS1p酶已获得了极大的兴趣，特别是涉及尿嘧啶和烟酰胺的抢救。的确,URS1p最初被归类为核苷水解酶（NH），对尿苷底物具有明显的偏好，但后来被证明也参与了Preiss-Handler依赖性途径，用于将内源性和外源性烟酰胺核苷（NR）再循环至NAD合成。这里,我们介绍了酵母URH1p酶的详细酶和结构表征，一类NH酶家族的成员。我们表明，URH1p对NR和尿苷的水解具有相似的催化效率，提倡该酶在NAD合成和核碱基补救中的双重作用。我们证明了URH1p的单体结构对于NH同源组I的成员来说是前所未有的，表明在该酶家族中N-核苷活性不严格需要寡聚化。大小,URH1p对合成底物5-氟尿苷的热稳定性和活性，抗肿瘤药物5-氟尿嘧啶的核苷前体，使这种酶成为一种有吸引力的工具，用于针对实体瘤的基因导向酶-前药激活疗法。
