The hpx Genetic System for Hypoxanthine Assimilation as a Nitrogen Source in Klebsiella pneumoniae: Gene Organization and Transcriptional Regulation
The hpx Genetic System for Hypoxanthine Assimilation as a Nitrogen Source in Klebsiella pneumoniae: Gene Organization and Transcriptional Regulation
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DOI：
10.1128/jb.01022-08
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发表时间：
2008-12-01
影响因子：
3.2
通讯作者：
Baldoma, Laura
中科院分区：
文献类型：
--
作者：
de la Riva, Lucia;Badia, Josefa;Baldoma, Laura
生长实验表明，在有氧条件下，多种肺炎菌株可以将腺嘌呤和低黄嘌呤用作氮源。从这些嘌呤中吸收的所有硝化物，表明分解代谢途径已完成，并经过艾伦托因（Allantoin）。在这里，我们确定了造成肺炎甲藻氨酸氧化为甲藻氨酸的遗传系统。 HPX群集由七个基因组成，其中提出了四个转录单元的组织，HPXDE，HPXR，HPXO和HPXPQT。与氧化（HPXDE）或尿酸（HPXO）氧化有关的蛋白质与已知催化这些反应的其他报道的酶没有任何相似性，而是与作用在芳族化合物上的氧酶相似。 HPX系统的表达通过氮的限制和特定底物的存在激活，HPXDE和HPXPQT由两个信号控制。 NTR系统介导了依赖于Sigma的HPXPQT转录的氮控制。相比之下，NTRC和氮同化控制蛋白都不参与HPXDE的氮控制，这取决于Sigma（70）进行转录。特定底物对这些操纵子的激活也是由不同的效应子和调节蛋白介导的。 HPXPQT的诱导需要形成尿酸，而HPXDE的表达是通过调节蛋白HPXR的低黄嘌呤诱导的。该LYSR型调节剂与基因间HPXD-HPXR区域中的TCTGC-N-4-GCAAA位点结合。当绑定到该站点以进行HPXDE激活时，HPXR会负面控制其自己的转录。
Growth experiments showed that adenine and hypoxanthine can be used as nitrogen sources by several strains of K. pneumoniae under aerobic conditions. The assimilation of all nitrogens from these purines indicates that the catabolic pathway is complete and proceeds past allantoin. Here we identify the genetic system responsible for the oxidation of hypoxanthine to allantoin in K. pneumoniae. The hpx cluster consists of seven genes, for which an organization in four transcriptional units, hpxDE, hpxR, hpxO, and hpxPQT, is proposed. The proteins involved in the oxidation of hypoxanthine (HpxDE) or uric acid (HpxO) did not display any similarity to other reported enzymes known to catalyze these reactions but instead are similar to oxygenases acting on aromatic compounds. Expression of the hpx system is activated by nitrogen limitation and by the presence of specific substrates, with hpxDE and hpxPQT controlled by both signals. Nitrogen control of hpxPQT transcription, which depends on sigma(54), is mediated by the Ntr system. In contrast, neither NtrC nor the nitrogen assimilation control protein is involved in the nitrogen control of hpxDE, which is dependent on sigma(70) for transcription. Activation of these operons by the specific substrates is also mediated by different effectors and regulatory proteins. Induction of hpxPQT requires uric acid formation, whereas expression of hpxDE is induced by the presence of hypoxanthine through the regulatory protein HpxR. This LysR-type regulator binds to a TCTGC-N-4-GCAAA site in the intergenic hpxD-hpxR region. When bound to this site for hpxDE activation, HpxR negatively controls its own transcription.