THE MALX-MALY OPERON OF ESCHERICHIA-COLI ENCODES A NOVEL ENZYME II OF THE PHOSPHOTRANSFERASE SYSTEM RECOGNIZING GLUCOSE AND MALTOSE AND AN ENZYME ABOLISHING THE ENDOGENOUS INDUCTION OF THE MALTOSE SYSTEM
THE MALX-MALY OPERON OF ESCHERICHIA-COLI ENCODES A NOVEL ENZYME II OF THE PHOSPHOTRANSFERASE SYSTEM RECOGNIZING GLUCOSE AND MALTOSE AND AN ENZYME ABOLISHING THE ENDOGENOUS INDUCTION OF THE MALTOSE SYSTEM
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DOI：
10.1128/jb.173.15.4862-4876.1991
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发表时间：
1991-08-01
影响因子：
3.2
通讯作者：
BOOS, W
中科院分区：
文献类型：
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作者：
REIDL, J;BOOS, W
缺乏MalK（结合蛋白依赖的麦芽糖-麦芽糖糊精运输系统的一个亚基）的突变体组成性地表达麦芽糖基因。马里的第二个位点突变消除了本构表达。malI基因（在连锁图谱上的36分钟处）编码一种典型的抑制蛋白，该蛋白与大肠杆菌LacI、GalR或CytR抑制蛋白同源（J. Reidl， K. Romisch， M. Ehrmann, and W. Boos， J.细菌学杂志，171:4888-4899,1989）。我们现在报道，马里调节一个相邻的和发散取向的操纵子包含malX和malY。malX编码一个分子量为56,654的蛋白，其氨基酸序列与葡萄糖磷酸转移酶系统II酶（ptsG）的同源性为34.9%，与n -乙酰氨基葡萄糖（nagE）的同源性为32.1%。当组成表达时，malX可以补充ptsG ptsM双突变体在葡萄糖上生长。同样，由于麦芽糖运输缺陷而无法在麦芽糖上生长的DELTA-malE malT（Con）菌株在引入malI::Tn10和携带malX的质粒后变成Mal+。malx介导的葡萄糖和麦芽糖的运输可能通过促进扩散发生。我们得出结论，malX编码一种磷酸转移酶系统II酶，该酶可以识别葡萄糖和麦芽糖作为底物，即使这些糖可能不代表该系统的天然底物。操纵子中的第二个基因malY编码一种43,500道尔顿的蛋白质。其氨基酸序列与转氨酶序列具有较弱的同源性。质粒编码的MalX单独存在足以补充在葡萄糖上的生长，质粒编码的MalX单独存在足以消除malK突变体中mal基因的组成。在野生型菌株中，malY基因的过度表达强烈地干扰了麦芽糖的生长。这种情况不是在一个malT（Con）菌株表达mal基因组成。我们得出结论，malY编码一种酶，可以降解麦芽糖系统的诱导剂或阻止其合成。
Mutants lacking MalK, a subunit of the binding protein-dependent maltose-maltodextrin transport system, constitutively express the maltose genes. A second site mutation in malI abolishes the constitutive expression. The malI gene (at 36 min on the linkage map) codes for a typical repressor protein that is homologous to the Escherichia coli LacI, GalR, or CytR repressor (J. Reidl, K. Romisch, M. Ehrmann, and W. Boos, J. Bacteriol. 171:4888-4899, 1989). We now report that MalI regulates an adjacent and divergently oriented operon containing malX and malY. malX encodes a protein with a molecular weight of 56, 654, and the deduced amino acid sequence of MalX exhibits 34.9% identity to the enzyme II of the phosphototransferase system for glucose (ptsG) and 32.1% identity to the enzyme II for N-acetylglucosamine (nagE). When constitutively expressed, malX can complement a ptsG ptsM double mutant for growth on glucose. Also, a DELTA-malE malT(Con) strain that is unable to grow on maltose due to its maltose transport defect becomes Mal+ after introduction of malI::Tn10 and the plasmid carrying malX. MalX-mediated transport of glucose and maltose is likely to occur by facilitated diffusion. We conclude that malX encodes a phosphotransferase system enzyme II that can recognize glucose and maltose as substrates even though these sugars may not represent the natural substrates of the system. The second gene in the operon, malY, encodes a protein of 43,500 daltons. Its deduced amino acid sequence exhibits weak homology to aminotransferase sequences. The presence of plasmid-encoded MalX alone was sufficient for complementing growth on glucose in a ptsM ptsG glk mutant, and the plasmid-encoded MalY alone was sufficient to abolish the constitutivity of the mal genes in a malK mutant. The overexpression of malY in a strain that is wild type with respect to the maltose genes strongly interferes with growth on maltose. This is not the case in a malT(Con) strain that expresses the mal genes constitutively. We conclude that malY encodes an enzyme that degrades the inducer of the maltose system or prevents its synthesis.