Cyclin A/cyclin-dependent kinase 2(CDK-2) complex
Homo sapiens (human)
The first protein kinase was discovered by the Japanese biochemist Nishizuka. When the complete genomes for organisms became available, they were analyzed to see what proteins they encode. It turned out that a very large number of genes, literally thousands, correspond to different protein kinases. Protein kinases may well comprise the most diverse protein family known. Protein kinases are involved in many activities of cell control as messengers of information. The overall structural core of all protein kinases is, despite their sequence diversity, very similar. They consist of two separate domains. The N-terminal domain, about one third of the core, contains mainly beta-sheet structure while the C-terminal domain contains a fairly large amount of alpha-helices. These two domains are connected by a short polypeptide region acting as a linker and allowing the two domains to move relative to one another. In a cleft formed by these two domains is a binding site for the molecule adenosine triphosphate (ATP). Protein kinases remove the last phosphate of ATP, turning it into ADP and attach the released phosphate to a group on another protein. They are therefore called phosphotransferases, proteins that transfer phosphate groups. There are three subfamilies: those that phosphorylate tyrosine residues of another protein, those that attach phosphate to serine or threonine residues and those that phosphorylate histidine. They are generally part of a large protein, containing both a kinase domain and a regulatory domain which controls the kinase activity. Cyclins are a family of proteins involved in the progression of cells through the cell cycle.
The protein shown here belongs to the subfamily of Ser/Thr protein kinases. Some kinases are inhibited by interaction of the regulatory subunit, others like the one here are activated by this action. Binding of the regulatory domain, cyclin, switches the protein on. The study of these proteins is presently very popular in pharmaceutical industry. The hope is that by inhibiting protein kinases one can control the signal flow within a cell and use this technique to cure diseases.
Protein Data Bank (PDB)
author: Arno Paehler