This entry represents RIO kinase, they exhibit little sequence similarity with eukaryotic protein kinases, and are classified as atypical protein kinases [ PUBMED:16183636 ]. The conformation of ATP when bound to the RIO kinases is unique when compared with ePKs, such as serine/threonine kinases or the insulin receptor … expand

This entry represents RIO kinase, they exhibit little sequence similarity with eukaryotic protein kinases, and are classified as atypical protein kinases [ PUBMED:16183636 ]. The conformation of ATP when bound to the RIO kinases is unique when compared with ePKs, such as serine/threonine kinases or the insulin receptor tyrosine kinase, suggesting that the detailed mechanism by which the catalytic aspartate of RIO kinases participates in phosphoryl transfer may not be identical to that employed in known serine/threonine ePKs. Representatives of the RIO family are present in organisms varying from Archaea to humans, although the RIO3 proteins have only been identified in multicellular eukaryotes, to date.

Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity [ PUBMED:3291115 ]:

• Serine/threonine-protein kinases
• Tyrosine-protein kinases
• Dual specificity protein kinases (e.g. MEK -phosphorylates both Thr and Tyr on target proteins)

Protein kinase function is evolutionarily conserved from Escherichia coli to human [ PUBMED:12471243 ]. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation [ PUBMED:12368087 ]. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved [ PUBMED:15078142 ], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [ PUBMED:15320712 ].