The eukaryotic protein kinases make up a large superfamily of homologous proteins. They are related by virtue of their kinase domains (also known as catalytic domains), which consist of ≈ 250‐300 amino acid residues. The kinase domains that define this group of enzymes contain 12 conserved subdomains that fold into a common catalytic core structure, as revealed by the 3‐dimensional structures of severed protein‐serine kinases. There are two main subdivisions within the superfamily: the protein‐serine/threonine kinases and the protein‐tyrosine kinases. A classification scheme can be founded on a kinase domain phylogeny, which reveals families of enzymes that have related substrate specificities and modes of regulation.—Hanks, S. K., Hunter, T. The eukaryotic protein kinase superfamily: kinase (catalytic) domain structure and classification. FASEB J. 9, 576‐596 (1995)
Hanks et al. (1995) studied this question.