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Gluconeogenic precursor availability regulates flux through the glyoxylate shunt in Pseudomonas aeruginosa

DOI: 10.1074/jbc.RA118.004514 DOI Help

Authors: Audrey Crousilles (University of Cambridge) , Stephen K. Dolan (University of Cambridge) , Paul Brear (University of Cambridge) , Dima Y. Chirgadze (University of Cambridge) , Martin Welch (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Biological Chemistry

State: Published (Approved)
Published: July 2018
Diamond Proposal Number(s): 9537 , 14043

Abstract: The glyoxylate shunt bypasses the oxidative decarboxylation steps of the tricarboxylic acid (TCA) cycle, thereby conserving carbon skeletons for gluconeogenesis and biomass production. In Escherichia coli, carbon flux is redirected through the first enzyme of the glyoxylate shunt, isocitrate lyase (ICL), following phosphorylation and inactivation of the TCA cycle enzyme, isocitrate dehydrogenase (ICD), by the kinase/phosphatase, AceK. In contrast, mycobacterial species lack AceK and employ a phosphorylation-insensitive isocitrate dehydrogenase (IDH), which is allosterically activated by the product of ICL activity, glyoxylate. However, Pseudomonas aeruginosa, expresses IDH, ICD, ICL, and AceK, raising the question of how these enzymes are regulated to ensure proper flux distribution between the competing pathways. Here, we present the structure, kinetics, and regulation of ICL, IDH, and ICD from P. aeruginosa. We found that flux partitioning is coordinated through reciprocal regulation of these enzymes, linking distribution of carbon flux to availability of the key gluconeogenic precursors, oxaloacetate and pyruvate. Specifically, a greater abundance of these metabolites activated IDH and inhibited ICL, leading to increased TCA cycle flux. Regulation was also exerted through AceK-dependent phosphorylation of ICD; high levels of acetyl-CoA (which would be expected to accumulate when oxaloacetate is limiting) stimulated the kinase activity of AceK, whereas high levels of oxaloacetate stimulated its phosphatase activity. In summary, the TCA cycle–glyoxylate shunt branch-point in P. aeruginosa has a complex enzymology which is profoundly different to that in other species characterized to date. Presumably, this reflects its predilection for consuming fatty acids, especially during infection scenarios.

Journal Keywords: glyoxylate shunt; Pseudomonas aeruginosa; isocitrate dehydrogenase; isocitrate lyase; metabolic regulation; bacterial metabolism; tricarboxylic acid cycle (TCA cycle) (Krebs cycle); enzyme structure; allosteric regulation; acetyl coenzyme A (acetyl-CoA)

Subject Areas: Biology and Bio-materials

Instruments: I02-Macromolecular Crystallography , I04-1-Macromolecular Crystallography (fixed wavelength)

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