Kinase

A kinase is an enzyme that catalyzes the transfer of a phosphate group from a high-energy donor, typically ATP, to a substrate. This phosphorylation alters the activity, interactions, localization, or stability of the target and is a central mechanism in many cellular signaling pathways and metabolic processes.

Kinases are diverse and can be classified by their substrates. Protein kinases phosphorylate amino acid residues on proteins; lipid kinases phosphorylate lipids; sugar kinases phosphorylate carbohydrates; and nucleotide kinases phosphorylate nucleotides. Protein kinases are further categorized by residue specificity into serine/threonine kinases, tyrosine kinases, and dual-specificity kinases that can act on more than one residue type.

Most kinases have a catalytic domain that binds ATP and the substrate. The gamma phosphate is transferred to the target residue, often regulated by an activation loop and other motifs that respond to cellular signals. Kinases frequently function within signaling cascades, where sequential phosphorylation events amplify and propagate messages that govern cell growth, differentiation, metabolism, and apoptosis.

Regulation of kinase activity is precise and multifaceted, involving phosphorylation and dephosphorylation, allosteric regulation, scaffolding interactions, and subcellular localization. Dysregulation of kinases is linked to diseases such as cancer, diabetes, and neurodegenerative disorders, making kinases prominent drug targets. Examples include protein kinases such as PKA, PKC, MAP kinases (ERK, JNK, p38), and receptor tyrosine kinases like EGFR, as well as non-receptor kinases such as Src and lipid kinases like PI3K. The term kinase encompasses any enzyme that transfers a phosphate from ATP to a substrate; enzymes that remove phosphate groups are phosphatases.