Regulation der Glutamatsynthese in Bacillus subtilis durch die Glutamatdehydrogenase RocG und das Aktivatorprotein GltC

Abstract

Bacillus subtilis is able to utilize a huge number of carbon sources. For efficient utilization of a carbon source both, carbon and nitrogen metabolism, have to be well coordinated. The synthesis of glutamate ist the link between both metabolic branches. The glutamate synthase (GOGAT) catalyzes the transfer of an amino group onto α-oxoglutarate, a key intermediate of the carbon metabolism. The synthesized glutamate serves as an amino group donor for the synthesis of other amino acids and nucleotides. In B. subtilis glutamate is exclusively synthesized by the GOGAT. In contrast to other bacteria the glutamate dehydrogenase (GDH) from B. subtilis is involved in glutamate degradation rather than in its synthesis. It is well known that the GOGAT is strongly expressed in presence of glucose to meet the increased requirement for glutamate, whereas the catabolic GDH is strongly repressed by glucose. In the absence of the preferred carbon source glucose the GDH is expressed and the expression of the GOGAT is inhibited. The expression of the GOGAT is dependent on the transcriptional activator protein GltC. In this work is shown that the GDH has two functions. Beside its enzymatic function the GDH is able to inactivate the activator protein GltC. The genetic data indicate that the catabolic GDH interacts with GltC. The inactivation of GltC by the GDH depends on the activity state of the glutamate degrading enzyme. The GDH has to be enzymatically active to inhibit the activator protein GltC. This unique regulatory mechanism allows the tight control of glutamate metabolism by the availability of carbon and nitrogen metabilism.