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首页> 外文期刊>Biochemistry >Escherichia coli UMP-kinase, a member of the aspartokinase family, is a hexamer regulated by guanine nucleotides and UTP.
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Escherichia coli UMP-kinase, a member of the aspartokinase family, is a hexamer regulated by guanine nucleotides and UTP.

机译：大肠杆菌UMP激酶是天冬氨酸激酶家族的成员，是一种受鸟嘌呤核苷酸和UTP调节的六聚体。

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摘要

The pyrH gene, encoding UMP-kinase from Escherichia coli, was cloned using as a genetic probe the property of the carAB operon to be controlled for its expression by the concentration of cytoplasmic UTP. The open reading frame of the pyrH gene of 723 bp was found to be identical to that of the smbA gene [Yamanaka, K., et al. (1992) J. Bacteriol. 174, 7517-7526], previously described as being involved in chromosome partitioning in E. coli. The bacterial UMP-kinase did not display significant sequence similarity to known nucleoside monophosphate kinases. On the contrary, it exhibited similarity with three families of enzymes including aspartokinases, glutamate kinases, and Pseudomonas aeruginosa carbamate kinase. UMP-kinase overproduced in E. coli was purified to homogeneity and analyzed for its structural and catalytic properties. The protein consists of six identical subunits, each of 240 amino acid residues (the N-terminal methionine residue is missing in the expressed protein). Upon excitation at 295nm, the bacterial enzyme exhibits a fluorescence emission spectrum with maximum at 332 nm which indicates that the single tryptophan residue of the protein (Trp119) is located in a hydrophobic environment. Like other enzymes involved in the de novo synthesis of pyrimidine nucleotides, UMP-kinase of E. coli is subject to regulation by nucleotides: GTP is an allosteric activator, whereas UTP serves as an allosteric inhibitor. UTP and UDP, but none of the other nucleotides tested such as GTP, ATP, and UMP, enhanced the fluorescence of the protein. The sigmoidal shape of the dose-response curve indicated cooperativity in binding of UTP and UDP.(ABSTRACT TRUNCATED AT 250 WORDS)
机译：使用作为遗传探针的carAB操纵子的特性克隆了pyHH基因，该蛋白编码来自大肠杆菌的UMP激酶，可通过细胞质UTP的浓度控制其表达。发现723bp的pyrH基因的开放阅读框与smbA基因的相同[Yamanaka，K。，等人。 （1992）J. Bacteriol。 174，7517-7526]，先前描述为参与大肠杆菌中的染色体分配。细菌UMP激酶与已知的核苷单磷酸激酶没有显着的序列相似性。相反，它表现出与三个酶家族的相似性，包括天冬氨酸激酶，谷氨酸激酶和铜绿假单胞菌氨基甲酸酯激酶。将在大肠杆菌中过量产生的UMP激酶纯化至均质，并对其结构和催化特性进行分析。该蛋白质由六个相同的亚基组成，每个亚基包含240个氨基酸残基（表达的蛋白质中缺少N末端甲硫氨酸残基）。在295nm激发后，细菌酶显示出最大332 nm处的荧光发射光谱，表明该蛋白（Trp119）的单个色氨酸残基位于疏水环境中。像其他参与嘧啶核苷酸从头合成的酶一样，大肠杆菌的UMP激酶也受核苷酸调节：GTP是一种变构激活剂，而UTP则是一种变构抑制剂。 UTP和UDP，但其他测试的核苷酸（如GTP，ATP和UMP）均未增强蛋白质的荧光。剂量-响应曲线的S形表明UTP和UDP的结合具有协同作用（摘要截断为250个字）

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