Anne Sexauer

• Signal transduction systems are of great importance for the adaptation of organisms to new conditions. These systems occur most frequently in bacteria and are well-understood thanks to research. It was not until 10 years after the discovery of two-component systems in bacteria that such a system was reported in archaea. This work provides new insights into signal transduction in archaea, through the characterization of a histidine kinase MA4377 and its multi-component system in the methanogenic archaeon Methanosarcina acetivorans. MA4377 is a hybrid kinase of bacterial origin and was probably integrated into M. acetivorans via horizontal gene transfer. Based on the fused receiver domains, MA4377 is classified as a hybrid kinase that regulates a cell response upon the perception of a signal through a multi-component system. These systems consist of four components, the first of which is the kinase. MA4377 has autophosphorylation activity and is phosphorylated at a conserved histidine residue (His497). While the kinase activity is independent of the redox state of the protein, the PAS domain is mandatory for autokinase activity. Using different protein variants, it could be shown that the two fused receiver domains are not involved in the phosphorelay. Rather, the single receiver domain MA4376 serves as the second component of the system. The signal is ultimately transmitted to a transcription factor (MA4375) of the Msr family. Factors of this family are involved in the regulation of methanogenesis, among other things. MA4377 could thus be involved in a multi-component system regulating methanogenesis. The receiver MA4376 plays a central role here since feedback regulation on the kinase was observed. Further investigations will show to what extent cross-regulation with other kinases takes place and in what way the receiver MA4376 plays a key role in this multi-component system.