Protein kinases are a group of enzymes that add a phosphate group to proteins to change their activity. In this process, ATP or GTP is the phosphate group donor, while serine and threonine and tyrosine protein kinases are the receptor. The protein kinase structure is complicated. The function domain of the protein kinase is conservative, which usurally consists of 250 ~ 300 amino acids. Protein kinase can be classified by two ways, one is classified by substrates, including tyrosine kinase, serine threonine kinase and histidine kinase. The other is classified by catalytic domains, including AGC kinase, CAMK kinase, CK1 kinase, CMGC kinase, STE kinase, Tyrosine Kinase and TKL kinase. Sometimes, protein kinase can be further subdivided into categories. As the member of cell signal chemical modification, protein kinases is particularly prominent in signal transduction and is known to regulate the majority of cell processes, such as metabolism, transcription, cell cycle progression, cell movement, apoptosis, and differentiation. Most kinases act on both serine and threonine, others act on tyrosine and a number of kinases act on all three amino acid residues. Serine/threonine protein kinases phosphorylate the OH group of serine or threonine amino acid residues. These protein kinases are usually stimulated by numerous chemical signals, including cAMP/cGMP, Ca2+/calmodulin, diacylglycerol. Tyrosine kinases that phosphorylate tyrosine amino acid residues act primarily as growth factor receptors. Protein kinase involves in several human diseases, including cancer, diabetes, autoimmune diseases and many other diseases. Therefore, properly regulating functions of protein kinases seem important for controlling these diseases. Abnormal activity of the protein kinase can cause disease, especially cancer. Protein kinases have emerged as one of the most frequently targeted families of proteins in drug discovery. In the past decades, the development of small molecule inhibitors of protein kinase also have gained remarkable successes in clinical research and cancer drugs.
Protein kinase can be classified by catalytic domains, including AGC kinase, CAMK kinase, CK1 kinase, CMGC kinase, STE kinase, TK kinase, TKL kinase and RGC kinase.
Protein kinase can be classified by substrates, including tyrosine kinase, serine threonine kinase, histidine kinase and cysteine kinase. Sometimes, protein kinase can be further subdivided into categories.