Abstract
Protein phosphorylation, one of the most important post-translational modifications, regulates almost every cellular process. Although signal transduction by protein phosphorylation is extensively studied in Eukaryotes and Bacteria, the knowledge of this process in archaea is greatly lagging behind, especially for Ser/Thr/Tyr phosphorylation by eukaryotic-like protein kinases (ePKs). So far, only a few studies on archaeal ePKs have been reported, most of which focused on the phosphorylation activities in vitro, but their physiological functions and interacting network are still largely unknown. In this study, we systematically investigated the autophosphorylation and cross-phosphorylation activities of ePKs from Sulfolobus islandicus REY15A using proteins expressed in Escherichia coli or S. islandicus. In vitro kinase assay showed that 7 out of the 11 putative ePKs have autophosphorylation activity. A protein Ser/Thr phosphatase, SiRe_1009, was able to dephosphorylate various autophosphorylated ePKs, confirming that these proteins are Ser/Thr kinases. Two ePKs, SiRe_2030 and SiRe_2056, homologs of typical eukaryotic PKs involved in peptide synthesis in response to various cellular stresses, exhibit highly efficient phosphorylation activities on both themselves and other ePKs. Overexpression of the protein kinases in vivo revealed that elevated level of either SiRe_1531 or SiRe_2056 inhibited the cell growth of S. islandicus cells. Finally, a phosphorylation network of the protein kinases was proposed and their putative physiological roles were discussed.
Highlights
Protein phosphorylation is a reversible post-translational modification that regulates almost all cellular processes, such as cell cycle progression, cell mobility, DNA replication and repair (Humphrey et al, 2015)
There are ten potential eukaryotic-like protein kinase (ePK) encoded in the S. solfataricus genome (Kennelly, 2014)
As S. islandicus has highly close phylogenetic relationship with S. solfataricus, the homologs of these 10 ePKs (SiRe_0101, SiRe_0171, SiRe_0181, SiRe_1057, SiRe_1531, SiRe_1570, SiRe_1810, SiRe_2030, SiRe_2056, and SiRe_2600) were all found in S. islandicus REY15A by
Summary
Protein phosphorylation is a reversible post-translational modification that regulates almost all cellular processes, such as cell cycle progression, cell mobility, DNA replication and repair (Humphrey et al, 2015). The activated forms of the former would recognize and phosphorylate the latter (Podgornaia and Laub, 2013) This linear signal transfer is different from the network regulatory pattern in eukaryotes. Recent studies on the eSTKs from Mycobacterium tuberculosis and the eSTKs and bacterial tyrosine kinases from Bacillus subtilis revealed that bacterial protein kinases exhibited both autophosphorylation and cross-phosphorylation activities on Ser, Thr, and Tyr residues. It seems that bacteria have a regulatory network and/or cascades of protein kinases as those in eukaryotes. It seems that bacteria have a regulatory network and/or cascades of protein kinases as those in eukaryotes. (Baer et al, 2014; Shi et al, 2014)
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