Signaltransduktion in $\textit{Corynebacterium glutamicum}$: Studien zur Rolle von Proteinen der FHA-Domäne

$\textit{Corynebacterium glutamicum}$ is an apathogenic soil bacterium, used for an annual production of up to 1,8 million tons L-glutamate and 0,9 million tons L-lysine. In the genome of $\textit{C. glutamicum}$ three genes have been annotated, which code for proteins with forkhead-associated (FHA) domains. One of these proteins named OdhI was recently shown to play an important role in the posttranslational regulation of the 2-oxoglutarate dehydrogenase (ODH) complex. In its unphosphorylated state the OdhI protein binds to the OdhA subunit of the ODH complex and thereby inhibits its activity. Phosphorylation of OdhI at Thr14 catalyzed by the serine/threonine protein kinase (STPK) PknG prevents interaction and ODH inhibition. In this thesis the interaction between OdhI and OdhA was further investigated. OdhI (15 kDa) is composed of a C-terminal FHA domain and a N-terminal extension, whereas OdhA (135 kDa) consists of a split 2-oxoglutarate dehydrogenase (E1) domain and an acyltrasferase (E2) domain, which are separated by a linker regions. Using different OdhI and OdhA length variants for $\textit{in vivo}$ copurification experiments and $\textit{in vitro}$ “surface plasmon resonance” (SPR) interaction studies, the interacting domains were narrowed down to the FHA domain of OdhI and the C-terminal E1 domain of OdhA. Furthermore it was confirmed, that phosphorylation of OdhI inhibits its interaction with OdhA. Despite the well characterized role of OdhI in regulation of ODH activity, its physiological function is still unknown. One reason for that is the missing knowledge of the stimulus, which triggers the phosphorylation of OdhI. Phosphorylation studies under different growth conditions suggested, that L-glutamine is an effector for OdhI phosphorylation. Growth analysis of a $\textit{C. glutamicum}$ $\Delta \textit{odhI}$ mutant in minimal medium with L-glutamine as sole carbon- and nitrogen-source pointed to further regulatory functions of OdhI. The second part of this thesis focussed on the characterization of the two other FHA domain proteins of $\textit{C. glutamicum}$, named FhaA and FhaB. The genomic localization of $\textit{fhaA}$ and $\textit{fhaB}$ in the gene cluster $\textit{fhaA-fhaB-ppp-rodA-pbpA-pknA-pknB-cg0055}$suggested that FhaA and FhaB could also be targets of STPKs and somehow involved in morphogenesis. Both $\textit{fhaA}$ and $\textit{fhaB}$ could be deleted, confirming that these genes are not essential. Analysis of the deletion mutants did not reveal an obvious link to morphogenesis. A growth phenotype of the strains $\Delta \textit{fhaA}$ and $\Delta \textit{fhaB}$ in minimal medium with L-glutamine as sole carbon- and nitrogen-source pointed to a possible regulatory function in glutamine metabolism. Copurification of FhaA with a FhaB derivative suggested an interaction between these proteins. Furthermore, dimerization and phosphorylation at threonine residues was demonstrated for both proteins