Lee Chang-Ro, Koo Byoung-Mo, Cho Seung-Hyon, Kim Yu-Jung, Yoon Mi-Jeong, Peterkofsky Alan, Seok Yeong-Jae
Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea.
Mol Microbiol. 2005 Oct;58(1):334-44. doi: 10.1111/j.1365-2958.2005.04834.x.
While the proteins of the phosphoenolpyruvate:carbohydrate phosphotransferase system (carbohydrate PTS) have been shown to regulate numerous targets, little such information is available for the nitrogen-metabolic phosphotransferase system (nitrogen-metabolic PTS). To elucidate the physiological role of the nitrogen-metabolic PTS, we carried out phenotype microarray (PM) analysis with Escherichia coli K-12 strain MG1655 deleted for the ptsP gene encoding the first enzyme of the nitrogen-metabolic PTS. Together with the PM data, growth studies revealed that a ptsN (encoding enzyme IIA(Ntr)) mutant became extremely sensitive to leucine-containing peptides (LCPs), while both ptsP (encoding enzyme I(Ntr)) and ptsO (encoding NPr) mutants were more resistant than wild type. The toxicity of LCPs was found to be due to leucine and the dephospho-form of enzyme IIA(Ntr) was found to be necessary to neutralize leucine toxicity. Further studies showed that the dephospho-form of enzyme IIA(Ntr) is required for derepression of the ilvBN operon encoding acetohydroxy acid synthase I catalysing the first step common to the biosynthesis of the branched-chain amino acids.
碳水化合物磷酸转移酶系统（碳水化合物PTS）的蛋白质已被证明可调节众多靶点，但关于氮代谢磷酸转移酶系统（氮代谢PTS）的此类信息却很少。为了阐明氮代谢PTS的生理作用，我们对编码氮代谢PTS第一种酶的ptsP基因缺失的大肠杆菌K-12菌株MG1655进行了表型微阵列（PM）分析。结合PM数据，生长研究表明，ptsN（编码酶IIA(Ntr)）突变体对含亮氨酸肽（LCPs）变得极其敏感，而ptsP（编码酶I(Ntr)）和ptsO（编码NPr）突变体均比野生型更具抗性。发现LCPs的毒性归因于亮氨酸，并且发现酶IIA(Ntr)的去磷酸化形式对于中和亮氨酸毒性是必需的。进一步研究表明，酶IIA(Ntr)的去磷酸化形式是解除对ilvBN操纵子的抑制所必需的，该操纵子编码催化支链氨基酸生物合成第一步的乙酰羟酸合酶I。
