Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Using the mini-Mu-duction technique, we cloned the malA regions from Escherichia coli K-12 and Klebsiella pneumoniae. A comparison of the structures of the cloned DNAs indicated that the malT, malP, and malQ genes, encoding the transcriptional activator of the maltose regulon, maltodextrin phosphorylase, and amylomaltase, respectively, are similarly organized in both species; malP and malQ constitute an operon divergent from the malT gene. We sequenced 1,200 nucleotides encompassing the beginnings of the malT and malP genes, their promoters, and the intergenic region. The DNA sequences from the two species were very different; the levels of homology ranged from 28 to 80%, depending on the region. The sequences of the coding regions and of elements known to be important for the functions of these two promoters in E. coli were well conserved between the two bacteria, whereas the sequence of the malT-malP intergenic region had totally diverged.
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PMID:Comparison of the malA regions of Escherichia coli and Klebsiella pneumoniae. 294 64

malZ is a member of the mal regulon. It is controlled by MatT, the transcriptional activator of the maltose system. MalZ has been purified and identified as an enzyme hydrolyzing maltotriose and longer maltodextrins to glucose and maltose. MalZ is dispensable for growth on maltose or maltodextrins. Mutants lacking amylomaltase (encoded by malQ), the major maltose utilizing enzyme, cannot grow on maltose, maltotriose, or maltotetraose, despite the fact that they contain an effective transport system and MalZ. From such a malQ mutant a pseudorevertant was isolated that was able to grow on maltose. The suppressor mutation was mapped in malZ. The mutant gene was cloned. It contained a Trp to Cys exchange at position 292 of the deduced protein sequence. Surprisingly, the purified mutant enzyme was still unable to hydrolyze maltose as was the wild type enzyme, while both were able to release glucose from maltodextrins. However, the mutant enzyme had gained the ability to transfer dextrinyl moieties to glucose, maltose, and other maltodextrins. Thus, it had gained an activity associated with amylomaltase. It was the MalZ292-associated transferase reaction that allowed the utilization of maltose. In addition, we discovered that mutant and wild type enzyme alike were highly active as gamma-cyclodextrinases.
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PMID:The MalT-dependent and malZ-encoded maltodextrin glucosidase of Escherichia coli can be converted into a dextrinyltransferase by a single mutation. 863 75

The maltose/maltodextrin regulon of Escherichia coli consists of 10 genes which encode a binding protein-dependent ABC transporter and four enzymes acting on maltodextrins. All mal genes are controlled by MalT, a transcriptional activator that is exclusively activated by maltotriose. By the action of amylomaltase, we prepared uniformly labeled [(14)C]maltodextrins from maltose up to maltoheptaose with identical specific radioactivities with respect to their glucosyl residues, which made it possible to quantitatively follow the rate of transport for each maltodextrin. Isogenic malQ mutants lacking maltodextrin phosphorylase (MalP) or maltodextrin glucosidase (MalZ) or both were constructed. The resulting in vivo pattern of maltodextrin metabolism was determined by analyzing accumulated [(14)C]maltodextrins. MalP(-) MalZ(+) strains degraded all dextrins to maltose, whereas MalP(+) MalZ(-) strains degraded them to maltotriose. The labeled dextrins were used to measure the rate of transport in the absence of cytoplasmic metabolism. Irrespective of the length of the dextrin, the rates of transport at a submicromolar concentration were similar for the maltodextrins when the rate was calculated per glucosyl residue, suggesting a novel mode for substrate translocation. Strains lacking MalQ and maltose transacetylase were tested for their ability to accumulate maltose. At 1.8 nM external maltose, the ratio of internal to external maltose concentration under equilibrium conditions reached 10(6) to 1 but declined at higher external maltose concentrations. The maximal internal level of maltose at increasing external maltose concentrations was around 100 mM. A strain lacking malQ, malP, and malZ as well as glycogen synthesis and in which maltodextrins are not chemically altered could be induced by external maltose as well as by all other maltodextrins, demonstrating the role of transport per se for induction.
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PMID:The maltodextrin system of Escherichia coli: metabolism and transport. 1632 36

MalT is the central transcriptional activator of all mal genes in Escherichia coli. Its activity is controlled by the inducer maltotriose. It can be inhibited by the interaction with certain proteins, and its expression can be controlled. We report here a novel aspect of mal gene regulation: the effect of cytoplasmic glucose and glucokinase (Glk) on the activity and the expression of MalT. Amylomaltase (MalQ) is essential for the metabolism of maltose. It forms maltodextrins and glucose from maltose or maltodextrins. We found that glucose above a concentration of 0.1 mM blocked the activity of the enzyme. malQ mutants when grown in the absence of maltodextrins are endogenously induced by maltotriose that is derived from the degradation of glycogen. Therefore, the fact that glk malQ(+) mutants showed elevated mal gene expression finds its explanation in the reduced ability to remove glucose from MalQ-catalyzed maltodextrin formation and is caused by a metabolically induced MalQ(-) phenotype. However, even in mutants lacking glycogen, Glk controls endogenous induction. We found that overexpressed Glk due to its structural similarity with Mlc, the repressor of malT, binds to the glucose transporter (PtsG), releasing Mlc and thus increasing malT repression. In addition, even in mutants lacking Mlc (and glycogen), the overexpression of glk leads to a reduction in mal gene expression. We interpret this repression by a direct interaction of Glk with MalT concomitant with MalT inhibition. This repression was dependent on the presence of either maltodextrin phosphorylase or amylomaltase and led to the inactivation of MalT.
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PMID:Glucose- and glucokinase-controlled mal gene expression in Escherichia coli. 1902