CaM kinase or CAMK family, also written as CaMK, is an abbreviation for the Ca2+/calmodulin-dependent protein kinase class of enzymes. CaMK represents a diverse group of protein kinases which activation is dependent on binding to Ca2+/calmodulin (CaM) complex. Based on substrate specificity, CaM kinases are divided into two groups, substrate restricted CaMKs and substrate multifunctional CaMKs. CaM kinases can be further categorized into the following subfamilies: CaMK I, CaMK II, CaMK III (Elongation Factor-2 Kinase), CaMK IV, phosphorylase kinase and myosin light chain kinase. CaMK I, II and IV have broader substrate specificity, and others are responsible for phosphorylation of a specific substrate.
CaMKs are activated by increases in the concentration of intracellular calcium ions (Ca2+) and transfers phosphates from ATP to defined serine or threonine residues in other proteins. Activated CaMK is involved in the phosphorylation of transcription factors and therefore, in the regulation of expression of responding genes.
Calcium ions as second messengers play an essential role in many important cellular processes. In plants, transient changes in calcium content in the cytosol (calcium signatures) have been observed during growth, development and under stress conditions. Such diverse functions require many different calcium sensors.
Generally, CaM kinases have an N-terminal kinase domain, an autoinhibitory domain and a CaM-binding domain. All CaM kinases require Ca2+/CaM binding for activation. The binding of Ca2+/CaM comlex results in release of the auto-inhibitory domain from catalytic domain, which allows further substrate access. Studies have shown that CaM kinase participate in activation of multiple targets, including Akt and NF-kB. Additionally, CaM kinases also have function in regulation of cell cycle. For example, CaM kinase II phosphorylates CDC25 which leads to an increase of CDC25 phosphatase activity.