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Authors: Strecker, Alexander
Title: Der C4-Dicarboxylat-Metabolismus von Escherichia coli : die Rolle von DcuA und von DcuS im Signaltransfer
Online publication date: 11-Dec-2018
Language: german
Abstract: The two-component-system DcuS-DcuR of Escherichia coli regulates the C4-dicarboxylate metabolism and consists of the membrane-integrated sensor DcuS and the response regulator DcuR. C4-dicarboxylates are detected by DcuS and transferred into a signal. After signal sensing via PASP, signal transduction occurs by a piston type movement of the transmembrane helix 2 across the membrane to the PASC domain. For the signal transduction in the cytoplasm, a transmission via the reduction of the dimerization of the PASC domain is postulated. In this work, structural changes between two functional states of DcuS (transition from responsive to activated state of the sensor) were investigated by hydrogen/deuterium mass spectrometry (HDX-MS). During signal transduction the accessibility of deuterium is increased in alpha helix 1 and decreased beta sheets 3 & 4. Thus, the structural changes are localized in the dimerization surface of PASC. HDX-MS studies validate the hypothesis of reduction of PASC dimerization during signal transduction. In addition to DctA and DcuB, Escherichia coli has other Dcu transporters for the uptake of C4-dicarboxylates. In this work an interaction within the Dcu transporters was investigated. An interaction between DcuA, DcuB, DcuC was identified by complexome profiling and confirmed by BACTH and mSPINE. A function for the interaction of the transporters could not be identified. DcuA is an alternative transporter of the main transporter DcuB for the uptake of C4-dicarboxylates under anaerobiosis. Since dcuA is constitutively expressed under aerobic and anaerobic conditions, DcuA has been postulated to function as an anaerobic transporter or as a transporter for the transition between aerobic and anaerobic conditions. In this work, DcuA was shown to be important for aerobic growth with L-aspartate as the sole nitrogen source, while DctA metabolizes L-aspartate as a carbon source. The transport of L-aspartate occurs via a symport or an antiport with C4-dicarboxylates. DcuA prefers L-aspartate to succinate in transport (KM = 43 and 844 micromolar, respectively) while DctA has a higher affinity for succinate compared to L-aspartate. When L-aspartate was the only source of nitrogen and glycerol the carbon source, L-aspartate was consumed, and equimolar amounts of fumarate or L-malate were excreted. These reactions were dependent on DcuA. L-aspartate was taken up in the amounts required for nitrogen metabolism but not for carbon metabolism. DcuA catalyzes an Laspartate/C4-dicarboxylate antiport and thus serves as an [N]-shuttle under aerobic conditions, with L-aspartate as sole nitrogen source.
DDC: 500 Naturwissenschaften
500 Natural sciences and mathematics
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 10 Biologie
Place: Mainz
Version: Original work
Publication type: Dissertation
License: in Copyright
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Extent: IX, 143 Seiten
Appears in collections:JGU-Publikationen

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