Authors:	Schubert, Christopher
Advisor:	Unden, Gottfried Heermann, Ralf
Title:	L-Aspartate is a high-quality nitrogen source of Escherichia coli: regulation and physiology
Online publication date:	18-Aug-2021
Year of first publication:	2021
Language:	english
Abstract:	Escherichia coli is a highly adaptable bacterium, which can utilize diverse carbon and nitrogen sources. In aerobic growth, the L-Asp transporter DcuA and the aspartate ammonia-lyase AspA catalyze a collaborative nitrogen shuttle in which L-Asp is transported into the bacterial cell and directly deaminated to form ammonium and fumarate. Ammonium is assimilated in the GS-GOGAT pathway, while fumarate is exported. In anaerobic growth, fumarate can be used to drive fumarate respiration, which transforms L-Asp to an elec-tron acceptor and nitrogen source, emphasizing the importance of L-Asp. AspA was stimulated by GlnB saturated with either 2-oxoglutarate and ATP, a bound UMP, or both. GlnB stimulates AspA deamination activity twofold, providing ammonium under nitrogen-limited conditions to supply the bacterial cell with a nitrogen source. The DcuA-AspA-GS-GOGAT pathway is able to produce L-Asp, L-Gln, L-Glu, and ammonium, which completely satisfies the nitrogen requirement of E. coli. L-Asp was found in millimolar concentration in the mouse intestine, which highlights its physiological relevance. DctA is an aerobic C4-dicarboxylate transporter which has a high affinity for succinate. Reporter gene assays of aspAp and dctAp expression, demonstrated a high sensitivity of the expression to the presence of different carbon sources, such as sugars, sugar alcohols, and C4-dicarboxylates. cAMP-CRP fine-tunes the expression of genes involved in the catabolism of substrates other than glucose, including aspA and dctA, in response to carbon availability. Bioinformatics revealed a mutation of the CRP-binding site in the dominant first half site of dctAp, explaining the higher repression in the presence of glycerol and D-xylose. In addition, DctA showed interaction with EIIAGlc of the glucose:phosphotransferase system, which is supposed to inhibit C4-dicarboxylate uptake in aerobic growth when upper and lower glycolytic substrates are available. Enzymes that catalyze sequential reactions in metabolic pathways can be organized into sequential complexes ('metabolons') capable of channeling metabolic intermediates and increasing metabolic efficiency. Interaction between DcuA-AspA, DcuB-AspA, and DcuB-FumB was demonstrated and was suggested to drive nitrogen assimilation and fumarate respiration. The sensor histidine kinase DcuS was modeled using various bioinformatic tools to investigate the interaction between the DcuS linker region and DctA helix 8b. The interaction model postulated a salt bridge between two residues to stabilize the interaction. In addition, the DcuS model, multiple sequence alignment, and current research indicated an L-Proline hinge in the N-terminal α-helix of the cytoplasmic PAS domain.
DDC:	570 Biowissenschaften 570 Life sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 10 Biologie
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-6262
URN:	urn:nbn:de:hebis:77-openscience-b7cba9f9-b1e9-41fc-b429-8e94e7c2d7071
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	http://rightsstatements.org/vocab/InC/1.0/
Extent:	166 Seiten
Appears in collections:	JGU-Publikationen