Nora Georgiev

• The ability of microorganisms to sense and react to environmental stimuli via signal transduction systems is a crucial factor in their survival. A variety of bacterial and eukaryotic signal transduction systems have been the subject of experimental investigations over the past few decades. Nevertheless, our understanding of archaeal signal transduction remains incomplete. At present, there are only a few publications that have experimentally investigated the structure and function of archaeal signalling. However, with the increasing number of fully sequenced archaeal genomes, there is an opportunity to examine these systems in greater detail. The methanogenic archaeon M. acetivorans has one of the largest known archaeal genomes and, with 53 putative HK and 16 putative RR, one of the largest sets of signal transduction systems. In a comprehensive study the histidine kinases and response regulators of the methanogenic archaeon M. acetivorans were first analysed in silico. This revealed that the HKs can be classified into four different groups with respect to their HK domain (MA_type 1 A/B/C, MA_type 2, MA_type 3 and MA_CheA). Afterwards four selected putative HK (RdmS, MA2082, MA2013 and MA4377) were studied in detail using a biochemical approach. The recombinant proteins were examined regarding their ATP binding affinity and their auto- and transphosphorylation activity was tested using radioactive autokinase assays. This revealed that three of the four proteins assayed are true autokinases and that RdmS is an unusual kinase lacking the H-box and autokinase activity.A phosphotransfer profiling assay of the three autokinases with all RRs encoded in the M. acetivorans genome revealed that the HK may interact with several RRs. In addition, MA4377 and MA2013 were identified as HHKs involved in phosphorelay systems. This study provided the first evidence for the existence of a complex signalling network in M. acetivorans involving multiple HKs and RRs.