Archaeal Signalling Networks—New Insights Into the Structure and Function of Histidine Kinases and Response Regulators of the Methanogenic Archaeon Methanosarcina acetivorans

The methanogenic archaeon Methanosarcina acetivorans has one of the largest known archaeal genomes. With 53 histidine kinases (HK), it also has the largest set of signal transduction systems. To gain insight into the hitherto not very well understood signal transduction in Archaea and M. acetivorans in particular, we have categorised the predicted HK into four types based on their H-box using an in silico analysis. Representatives of three types were recombinantly produced in Escherichia coli and purified by affinity chromatography. All investigated kinases showed ATP binding and hydrolysis. The MA_type 2 kinase, which lacks the classical H-box, showed no autokinase activity. Furthermore, we could show that M. acetivorans possesses an above-average number of response regulators (RR), consisting of only a REC domain (REC-only). Using the hybrid kinase MA4377 as an example we show that both intra-and intermolecular transphosphorylation to REC domains occur. These experiments are furthermore indicative of complex phosphorelay systems in M. acetivorans and suggest that REC-only proteins act as a central hub in signal transduction in M. acetivorans.