Activation of SsoPK4, an Archaeal eIF2α Kinase Homolog, by Oxidized CoA.

The eukaryotic protein kinase (ePK) paradigm provides integral components for signal transduction cascades throughout nature However, while so-called typical ePKs permeate the and atypical ePKs dominate the kinomes of the . Intriguingly, the catalytic domains of the handful of deduced typical ePKs from the archaeon P2 exhibit significant resemblance to the protein kinases that phosphorylate translation initiation factor 2α (eIF2α) in response to cellular stresses. We cloned and expressed one of these archaeal eIF2α protein kinases, SsoPK4.

The activity of an ancient atypical protein kinase is stimulated by ADP-ribose in vitro.

The piD261/Bud32 protein kinases are universal amongst the members of the Eucarya and Archaea. Despite the fact that phylogenetic analyses indicate that the piD261/Bud32 protein kinases descend directly from the primordial ancestor of the "eukaryotic" protein kinase superfamily, our knowledge of their physiological role is relatively fragmentary and largely limited to two eucaryal representatives: piD261/Bud32 from yeast and the p53-related protein kinase from humans. A deduced archaeal homolog, SsoPK5, is encoded by open reading frame sso0433 from the acidothermophile Sulfolobus solfataricus.

An arsenate reductase from Synechocystis sp. strain PCC 6803 exhibits a novel combination of catalytic characteristics.

The deduced protein product of open reading frame slr0946 from Synechocystis sp. strain PCC 6803, SynArsC, contains the conserved sequence features of the enzyme superfamily that includes the low-molecular-weight protein-tyrosine phosphatases and the Staphylococcus aureus pI258 ArsC arsenate reductase. The recombinant protein product of slr0946, rSynArsC, exhibited vigorous arsenate reductase activity (V(max) = 3.