Sunday, July 26, 2009
P127
Citric acid cycle regulation in Corynebacterium glutamicum and its implications for metabolic engineering
Meike Baumgart, Christian G. Schultz, Axel Niebisch, and Michael Bott. Institute of Biotechnology 1, Forschungszentrum Juelich GmbH, Leo Brandt Strassee, Juelich, 52425, Germany
The Gram-positive soil bacterium Corynebacterium glutamicum is used industrially for production of amino acids such as L-glutamate and L-lysine. The tricarboxylic acid cycle (TCA cycle) is a central metabolic pathway which, besides its function in energy generation, provides the biosynthetic precursors for glutamate and lysine. In order to improve production strains of C. glutamicum, it is necessary to have a detailed knowledge of the TCA cycle enzymes and regulatory mechanisms. This was subject of intensive investigations in the past years revealing that C. glutamicum contains a very complex regulatory network acting at the transcriptional and posttranscriptional level. Aconitase (Acn) is one example for extensive regulation at the transcriptional level by at least three regulators, namely AcnR, RipA and RamA. A deletion of acn or icd (coding for isocitrate dehydrogenase) was found to be very often associated with inactivating mutations in a second TCA cycle gene. The 2-oxoglutarate dehydrogenase complex (ODHc) is controlled at the posttranscriptional level. ODHc is inhibited by the unphosphorylated form of the regulatory protein OdhI and phosphorylation relieves inhibition. The phosphorylation status of OdhI is controlled by up to four serine/threonine protein kinases and one phosphatase. Glutamate production critically depends on a reduced ODHc activity and was found to be strongly inhibited in a mutant lacking OdhI but improved in a mutant lacking serine/threonine protein kinase PknG.
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