Regulation of glutamate metabolism by protein kinases in mycobacteria

Mol Microbiol. 2008 Dec;70(6):1408-23. doi: 10.1111/j.1365-2958.2008.06489.x. Epub 2008 Oct 17.

Abstract

Protein kinase G of Mycobacterium tuberculosis has been implicated in virulence and in regulation of glutamate metabolism. Here we show that this kinase undergoes a pattern of autophosphorylation that is distinct from that of other M. tuberculosis protein kinases characterized to date and we identify GarA as a substrate for phosphorylation by PknG. Autophosphorylation of PknG has little effect on kinase activity but promotes binding to GarA, an interaction that is also detected in living mycobacteria. PknG phosphorylates GarA at threonine 21, adjacent to the residue phosphorylated by PknB (T22), and these two phosphorylation events are mutually exclusive. Like the homologue OdhI from Corynebacterium glutamicum, the unphosphorylated form of GarA is shown to inhibit alpha-ketoglutarate decarboxylase in the TCA cycle. Additionally GarA is found to bind and modulate the activity of a large NAD(+)-specific glutamate dehydrogenase with an unusually low affinity for glutamate. Previous reports of a defect in glutamate metabolism caused by pknG deletion may thus be explained by the effect of unphosphorylated GarA on these two enzyme activities, which may also contribute to the attenuation of virulence.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Carboxy-Lyases / antagonists & inhibitors
  • Carboxy-Lyases / metabolism
  • Cyclic GMP-Dependent Protein Kinases / genetics
  • Cyclic GMP-Dependent Protein Kinases / metabolism*
  • Glutamate Dehydrogenase / metabolism
  • Glutamic Acid / metabolism*
  • Molecular Sequence Data
  • Mycobacterium smegmatis / metabolism
  • Mycobacterium tuberculosis / enzymology*
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / growth & development
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / metabolism*

Substances

  • Glutamic Acid
  • Glutamate Dehydrogenase
  • PknB protein, Mycobacterium tuberculosis
  • Protein-Serine-Threonine Kinases
  • Cyclic GMP-Dependent Protein Kinases
  • Carboxy-Lyases
  • 2-oxoglutarate decarboxylase