REGULATION OF ANAEROBIC CITRATE METABOLISM IN KLEBSIELLA-PNEUMONIAE
REGULATION OF ANAEROBIC CITRATE METABOLISM IN KLEBSIELLA-PNEUMONIAE
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DOI：
10.1111/j.1365-2958.1995.mmi_18030533.x
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发表时间：
1995-11-01
影响因子：
3.6
通讯作者：
DIMROTH, P
中科院分区：
文献类型：
--
作者：
BOTT, M;MEYER, M;DIMROTH, P
在厌氧条件下，肺炎克雷伯氏菌摄取和催化柠檬酸盐特别需要三种酶：Na+依赖性柠檬酸盐载体（CitS）、柠檬酸盐裂解酶（CitDEF）和Na+泵草酰乙酸脱羧酶（OadGAB）。相应的基因聚集在染色体上，其中citCDEFG基因位于citS-oadGAB基因的上游并且与citS-oadGAB基因趋异。我们发现，在大肠杆菌中从其天然启动子表达citS需要oadB下游的DNA区域。该区域的核苷酸序列分析揭示了两个相邻基因citA和citB的存在。通过序列相似性分析，推测CitA和CitB蛋白属于双组分调节系统。传感激酶CitA的N端含有两个跨膜螺旋，其中包含一个约130个氨基酸的周质结构域。当用柠檬酸盐加甘油厌氧培养时，所有柠檬酸盐特异性发酵酶在野生型中合成，但在citS突变体中不合成。这表明citS、oadGAB和citDEF需要CitB蛋白表达，因此是调节子的一部分，在野生型中，CitS、草酰乙酸脱羧酶和柠檬酸裂解酶的合成依赖于柠檬酸盐、钠离子和低氧张力的存在。在以高水平组成型表达CitS的citA无效突变体中，这些信号中没有一个是形成柠檬酸盐发酵酶所需的。结果表明，柠檬酸盐、Na+和氧通过CitA/CitB系统发挥调控作用，在这些信号存在下，citAB基因产物诱导自身合成，citAB与citS和oadGAB共转录产生正性自身调节。
Three enzymes are specifically required for uptake and catabolism of citrate by Klebsiella pneumoniae under anaerobic conditions: a Na+-dependent citrate carrier (CitS), citrate lyase (CitDEF), and the Na+ pump oxaloacetate decarboxylase (OadGAB). The corresponding genes are clustered on the chromosome, with the citCDEFG genes located upstream and divergent to the citS-oadGAB genes, We found that expression of citS from its native promoter in Escherichia coli requires the DNA region downstream of oadB. Nucleotide sequence analysis of this region revealed the presence of two adjacent genes, citA and citB. By sequence similarity, the predicted CitA and CitB proteins were identified as members of the two-component regulatory systems, The sensor kinase CitA contained, in the N-terminal half, two putative transmembrane helices which enclosed a presumably periplasmic domain of about 130 amino acids, The C-terminal half of the response regulator CitB harboured a helix-turn-helix motif typical of DNA-binding proteins, K. pneumoniae citB null mutants were unable to grow anaerobically with citrate as the sole carbon and energy source (Cit(-) phenotype), When cultivated anaerobically with citrate plus glycerol, all of the citrate-specific fermentation enzymes were synthesized in the wild type, but not in the citS mutants, This showed that citS, oadGAB and citDEF required the CitB protein for expression and therefore are part of a regulon, In the wild type, synthesis of CitS, oxaloacetate decarboxylase and citrate lyase was dependent on the presence of citrate, sodium ions and a low oxygen tension, In a citA null mutant which expressed citS constitutively at high levels, none of these signals was required for the formation of the citrate fermentation enzymes. This result suggested that citrate, Na+, and oxygen exerted their regulatory effects via the CitA/CitB system, In the presence of these signals, the citAB gene products induced their own synthesis, The positive autoregulation occurred via co-transcription of citAB with citS and oadGAB.