Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 284, Issue 1, Pages 265-275Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M807856200
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- Deutsche Forschungsgemeinschaft
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DcuB of Escherichia coli catalyzes C-4-dicarboxylate/succinate antiport during growth by fumarate respiration. The expression of genes of fumarate respiration, including the genes for DcuB (dcuB) and fumarate reductase (frdABCD) is transcriptionally activated by C-4-dicarboxylates via the DcuS-DcuR two-component system, comprising the sensor kinase DcuS, which contains a periplasmic sensing domain forC(4)-dicarboxylates. Deletion or inactivation of dcuB caused constitutive expression of DcuS-regulated genes in the absence of C-4-dicarboxylates. The effect was specific for DcuB and not observed after inactivation of the homologous DcuA or the more distantly related DcuC transporter. Random and site-directed mutation identified three point mutations (T394I, D398N, and K353A) in DcuB that caused a similar derepression as dcuB deletion, whereas the transport activity of the DcuB mutants was retained. Constitutive expression in the dcuB mutants depended on the presence of a functional DcuS-DcuR two-component system. Mutation of residues E79A, R83A, and R127A of DcuB, on the other hand, inactivated growth by fumarate respiration and transport of [C-14] succinate, whereas the expression of dcuB'-lacZ was not affected. Therefore, the antiporter DcuB is a bifunctional protein and has a regulatory function that is independent from transport, and sites for transport and regulation can be differentiated.
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