Regulation of NAD synthesis by the trifunctional NadR protein of Salmonella enterica
Regulation of NAD synthesis by the trifunctional NadR protein of Salmonella enterica
复制标题
DOI：
10.1128/jb.187.8.2774-2782.2005
复制
发表时间：
2005-04-01
影响因子：
3.2
通讯作者：
Roth, JR
中科院分区：
文献类型：
--
作者：
Grose, JH;Bergthorsson, U;Roth, JR
NadR的三种活性在纯化的蛋白质中被证明，并通过错义突变被分配到不同的结构域。N-末端结构域抑制NAD合成和补救基因的转录。C-末端结构域具有烟酰胺核糖激酶（NmR-K; EC www.example.com）活性，其对于NmR的同化是必需的，将其内部转化为烟酰胺单核苷酸（NMN）。中心结构域具有弱腺苷酰转移酶（NMN-AT; EC www.example.com）活性，其将NMN直接转化为NAD，但在生理学上不相关。该中心域介导NAD对所有NadR活动的调节作用。在没有效应子的情况下，纯NadR蛋白结合操纵基因DNA（默认状态），并由ATP释放（预期存在于体内）。NAD允许NadR在ATP存在下结合DNA并在体内引起抑制。超阻遏突变改变了中央（NMN-AT）结构域中的ATP结合残基。这消除了NMN-AT活性，并将酶置于其默认（DNA结合）状态。突变蛋白显示出完整的NmR激酶活性，其对NAD抑制的敏感性比野生型高10倍。有人提出，NAD和超阻遏突变发挥其作用，阻止ATP结合的中央域。
The three activities of NadR were demonstrated in purified protein and assigned to separate domains by missense mutations. The N-terminal domain represses transcription of genes for NAD synthesis and salvage. The C-terminal domain has nicotinamide ribose kinase (NmR-K; EC 2.7.1.22) activity, which is essential for assimilation of NmR, converting it internally to nicotinamide mononucleotide (NMN). The central domain has a weak adenylyltransferase (NMN-AT; EC 2.7.7.1) activity that converts NMN directly to NAD but is physiologically irrelevant. This central domain mediates regulatory effects of NAD on all NadR activities. In the absence of effectors, pure NadR protein binds operator DNA (the default state) and is released by ATP (expected to be present in vivo). NAD allows NadR to bind DNA in the presence of ATP and causes repression in vivo. A superrepressor mutation alters an ATP-binding residue in the central (NMN-AT) domain. This eliminates NMN-AT activity and places the enzyme in its default (DNA binding) state. The mutant protein shows full NmR kinase activity that is 10-fold more sensitive to NAD inhibition than the wild type. It is proposed that NAD and the superrepressor mutation exert their effects by preventing ATP from binding to the central domain.