Functional plasticity and allosteric regulation of α-ketoglutarate decarboxylase in central mycobacterial metabolism.
ABSTRACT The α-ketoglutarate dehydrogenase (KDH) complex is a major regulatory point of aerobic energy metabolism. Mycobacterium tuberculosis was reported to lack KDH activity, and the putative KDH E1o component, α-ketoglutarate decarboxylase (KGD), was instead assigned as a decarboxylase or carboligase. Here, we show that this protein does in fact sustain KDH activity, as well as the additional two reactions, and these multifunctional properties are shared by the Escherichia coli homolog, SucA. We also show that the mycobacterial enzyme is finely regulated by an additional acyltransferase-like domain and by the action of acetyl-CoA, a powerful allosteric activator able to enhance the concerted protein motions observed during catalysis. Our results uncover the functional plasticity of a crucial node in bacterial metabolism, which may be important for M. tuberculosis during host infection.
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ABSTRACT: Background Genome evolution in intracellular microbial symbionts is characterized by gene loss, generating some of the smallest and most gene-poor genomes known. As a result of gene loss these genomes commonly contain metabolic pathways that are fragmented relative to their free-living relatives. The evolutionary retention of fragmented metabolic pathways in the gene-poor genomes of endosymbionts suggests that they are functional. However, it is not always clear how they maintain functionality. To date the fragmented metabolic pathways of endosymbionts have been shown to maintain functionality through complementation by host genes, complementation by genes of another endosymbiont and complementation by genes in host genomes that have been horizontally acquired from a microbial source that is not the endosymbiont. Here we demonstrate a fourth mechanism.ResultsWe investigate the evolutionary retention of a fragmented pathway for the essential nutrient pantothenate (vitamin B5) in the pea aphid, Acyrthosiphon pisum endosymbiosis with Buchnera aphidicola. Using quantitative analysis of gene expression we present evidence for complementation of the Buchnera pantothenate biosynthesis pathway by host genes. Further, using complementation assays in an Escherichia coli mutant we demonstrate functional replacement of a pantothenate biosynthesis enzyme, 2-dehydropantoate 2-reductase (E.C. 22.214.171.124), by an endosymbiont gene, ilvC, encoding a substrate ambiguous enzyme.Conclusions Earlier studies have speculated that missing enzyme steps in fragmented endosymbiont metabolic pathways are completed by adaptable endosymbiont enzymes from other pathways. Here we experimentally demonstrate completion of a fragmented endosymbiont vitamin biosynthesis pathway by recruitment of a substrate ambiguous enzyme from another pathway. In addition this work extends host/symbiont metabolic collaboration in the aphid/Buchnera symbiosis from amino acid metabolism to include vitamin biosynthesis.BMC Biology 12/2014; 12(1):110. DOI:10.1186/s12915-014-0110-4 · 7.43 Impact Factor
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ABSTRACT: In order to survive and compete in natural settings, bacteria must excel at quickly adapting their metabolism to fluctuations in nutrient availability and other environmental variables. This necessitates fast-acting post-translational regulatory mechanisms, that is, allostery or covalent modification, to control metabolic flux. While allosteric regulation has long been a well-established strategy for regulating metabolic enzyme activity in bacteria, covalent post-translational modes of regulation, such as phosphorylation or acetylation, have previously been regarded as regulatory mechanisms employed primarily by eukaryotic organisms. Recent findings, however, have shifted this perception and point to a widespread role for covalent posttranslational modification in the regulation of metabolic enzymes and fluxes in bacteria. This review provides an outline of the exciting recent advances in this area. Copyright © 2015 Elsevier Ltd. All rights reserved.Current Opinion in Microbiology 04/2015; 24. DOI:10.1016/j.mib.2014.12.006 · 7.22 Impact Factor
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ABSTRACT: Metabolism underpins the physiology and pathogenesis of Mycobacterium tuberculosis. However, although experimental mycobacteriology has provided key insights into the metabolic pathways that are essential for survival and pathogenesis, determining the metabolic status of bacilli during different stages of infection and in different cellular compartments remains challenging. Recent advances-in particular, the development of systems biology tools such as metabolomics-have enabled key insights into the biochemical state of M. tuberculosis in experimental models of infection. In addition, their use to elucidate mechanisms of action of new and existing antituberculosis drugs is critical for the development of improved interventions to counter tuberculosis. This review provides a broad summary of mycobacterial metabolism, highlighting the adaptation of M. tuberculosis as specialist human pathogen, and discusses recent insights into the strategies used by the host and infecting bacillus to influence the outcomes of the host-pathogen interaction through modulation of metabolic functions. Copyright © 2014 Cold Spring Harbor Laboratory Press; all rights reserved.Cold Spring Harbor Perspectives in Medicine 12/2014; DOI:10.1101/cshperspect.a021121 · 7.56 Impact Factor