kinase

A kinase is an enzyme that acts like a molecular light switch, flipping other proteins on or off by attaching a small phosphate tag to them. This act of tagging, called phosphorylation, changes the target protein's shape or activity. Because cells use these switches to control growth, division, and survival, kinases sit at the heart of cellular signaling.

Mechanically, a kinase grabs a molecule of ATP, the cell's energy currency, and transfers one of its phosphate groups onto a specific spot on a substrate protein. The human genome encodes more than five hundred kinases, and they all share a similar ATP-binding pocket. That shared pocket is both an opportunity and a problem: it gives medicinal chemists a clear place to aim, but it makes selectivity between kinases hard.

Kinases became famous as cancer drug targets because faulty, overactive kinases can drive tumors to grow uncontrollably. Many kinase inhibitors work by sitting in the ATP pocket and blocking phosphate transfer. The honest caveat is that tumors often mutate the kinase so the drug no longer fits, which is why later-generation and allosteric inhibitors are continually developed.