Affiliation:
1. Department of Biology, University of Konstanz, 78457 Konstanz, Germany
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Reference62 articles.
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