Glutamate production by Corynebacterium glutamicum: dependence on the oxoglutarate dehydrogenase inhibitor protein OdhI and protein kinase PknG

Abstract

We recently showed that the activity of the 2-oxoglutarate dehydrogenase complex (ODHC) in Corynebacterium glutamicum is controlled by a novel regulatory mechanism that involves a 15-kDa protein called OdhI and serine/threonine protein kinase G (PknG). In its unphosphorylated state, OdhI binds to the E1 subunit (OdhA) of ODHC and, thereby, inhibits its activity. Inhibition is relieved by phosphorylation of OdhI at threonine-14 by PknG under conditions requiring high ODHC activity. In this work, evidence is provided that the dephosphorylation of phosphorylated OdhI is catalyzed by a phospho-Ser/Thr protein phosphatase encoded by the gene cg0062, designated ppp. As a decreased ODHC activity is important for glutamate synthesis, we investigated the role of OdhI and PknG for glutamate production under biotin limitation and after addition of Tween-40, penicillin, or ethambutol. A DeltaodhI mutant formed only 1-13% of the glutamate synthesized by the wild type. Thus, OdhI is essential for efficient glutamate production. The effect of a pknG deletion on glutamate synthesis was dependent on the induction conditions. Under strong biotin limitation and in the presence of ethambutol, the DeltapknG mutant showed significantly increased glutamate production, offering a new way to improve production strains.

Overproduction of l-Glutamate in Corynebacterium glutamicum

“…A novel mode of ODHC activity regulation has also been reported recently. ODHC activity was strongly inhibited by the nonphosphorylated form of OdhI protein, which is phosphorylated by serine/threonine protein kinases, including PknG and PknB, and is dephosphorylated by a phosphoserine/threonine protein phosphatase Ppp (Niebisch et al 2006;Schultz et al 2007). OdhI, encoded by cg1630, is a 15-kDa protein identified as an in vivo substrate of PknG.…”

Analysis and Engineering of Metabolic Pathway Fluxes in Corynebacterium glutamicum

“…The flux through pyruvate carboxylase strongly increased under glutamate production induced by Tween 40 addition, while PEP carboxylase and PEP carboxykinase fluxes remained constant. An impressive set of studies investigated the metabolism within the TCA cycle linked to glutamate production in great detail [4,117,157,158]. Successful strategies to increase glutamate production involved deletion of odhA, encoding a key protein of the complex [159] or attenuation of odhA expression via the use of antisense RNA [160].…”

“…With the advent of recombinant DNA technology, targeted genetic engineering of C. glutamicum became available and was successfully used to derive improved production properties. Today, C. glutamicum is applied to the industrial production of glutamate as flavor enhancer in human nutrition (1.5 million tons per year), [4], lysine (850,000 tons per year) [5] as well as tryptophan (10,000 tons per year) as additive in animal feed [6]. The improvement of existing production strains focuses on higher yield and productivity, better stress tolerance, or a broader substrate spectrum.…”

Metabolic Networking through Enzymatic Sensing, Signaling and Response to Homeostatic Fluctuations

“…However, the overall control of the processes is changed in such a way that the oxidation of both substrates is regulated not separately, but together within one complex. The chimeric complex also has a very unusual regulation through posttranslational modification of a specific regulatory protein (Schultz et al, 2007, Niebisch et al, 2006. This example illustrates that the species-specific organization of metabolic networks and their coordination mechanisms greatly affect the catalysts evolved in living systems.…”