GlnK Facilitates the Dynamic Regulation of Bacterial Nitrogen Assimilation

Adam Gosztolai, Jorg Schumacher, Volker Behrends, J.G. Bundy, Franziska Heydenreich, Mark H. Bennett, Martin Buck, Mauricio Barahona

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Abstract

Ammonium assimilation in Escherichia coli is regulated by two paralogous proteins (GlnB and GlnK), which orchestrate interactions with regulators of gene expression, transport proteins, and metabolic pathways. Yet how they conjointly modulate the activity of glutamine synthetase, the key enzyme for nitrogen assimilation, is poorly understood. We combine experiments and theory to study the dynamic roles of GlnB and GlnK during nitrogen starvation and upshift. We measure time-resolved in vivo concentrations of metabolites, total and posttranslationally modified proteins, and develop a concise biochemical model of GlnB and GlnK that incorporates competition for active and allosteric sites, as well as functional sequestration of GlnK. The model predicts the responses of glutamine synthetase, GlnB, and GlnK under time-varying external ammonium level in the wild-type and two genetic knock-outs. Our results show that GlnK is tightly regulated under nitrogen-rich conditions, yet it is expressed during ammonium run-out and starvation. This suggests a role for GlnK as a buffer of nitrogen shock after starvation, and provides a further functional link between nitrogen and carbon metabolisms.

© 2017 Biophysical Society.
This is an open access article under the CC BY license (http://
creativecommons.org/licenses/by/4.0/).
Original languageEnglish
Pages (from-to)2219
Number of pages2230
JournalBIOPHYSICAL JOURNAL
Volume112
Issue number10
DOIs
Publication statusPublished - 23 May 2017

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