Unravelling archaeal signal transduction networks

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Reversible protein phosphorylation is the main mechanism of signal transduction that enables cells to rapidly respond to environmental changes by controlling the functional properties of proteins in response to external stimuli. Compared to our knowledge of protein phosphorylation in Eukaryotes and Bacteria, little is still known about this process in the third domain of life, the Archaea. Crenarchaeota depend on protein phosphorylation on Ser, Thr and Tyr by Hanks (eukaryotic)-type protein kinases and common bacterial-type two component systems (phosphorylation on His and Asp) are absent. To gain first insights into the role of protein phosphorylation in archaea, the phoshoproteome of two members of the Sulfolobales were analyzed. These studies revealed a high amount of phospho-proteins with an unexpected high number of tyrosine phosphorylation and major changes in protein phosphorylation in response to carbon source (Sulfolobus solfataricus) as well as protein phosphatase deletion (S. acidocaldarius). Deletion of the two identified protein phosphatases, Saci-PTP and Saci-PP2A, in S. acidocaldarius resulted in no obvious phenotype for the Saci-PTP, however, deletion of Saci-PP2A led to enlarged cells and hypermotility in swarming assays. Based on this study, we identified a number of regulators and other factors that influence the expression of the archaellum, the archaeal motility structure, in a protein phosphorylation dependent manner. To further unravel the physiological function of protein phosphatases and protein kinases the enzymes from S. acidocaldarius were expressed and the respective deletion strains were constructed. This approach allowed for first insights into the regulation of the archaellum regulatory network and central carbohydrate metabolism by signal transduction. In future studies we will continue to investigate the different players of the regulatory (de)phosphorylation network. Further on we will study the interplay of the different players in order to unravel the hierarchical structures of these networks.