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 []:Serine/threonine-protein kinasesTyrosine-protein kinasesDual 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 []. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation []. 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 [], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [].TESK1 (testis-specific protein kinase 1) is a protein kinase with a structure composed of an N-terminal protein kinase domain and a C-terminal proline-rich domain and is most closely related to the LIM motif-containing protein kinase (LIMK) subfamily []. TESK1 has kinase activity with dual specificity on both serine/threonine and tyrosine residues []. When expressed in HeLa cells, TESK1 stimulates the formation of actin stress fibres and focal adhesions and functions downstream of integrins through phosphorylation and inactivation of cofilin []. In a yeast two-hybrid screen, Sprouty4 was identified as a binding partner of TESK1 [], and was subsequently found to negatively regulate cell spreading by inhibiting the kinase activity of TESK1 [].
