Protein phosphatases are enzymes that remove phosphate groups that have been attached to amino acid residues of proteins by protein kinases. The phosphates are important in signal transduction by regulating the proteins they are attached to. To reverse the regulatory effect, the phosphate has to be removed. This occurs on its own by hydrolysis or is mediated by protein phosphatases.
Serine/threonine-specific protein phosphatases
Serine and threonine phosphates are stable under physiological conditions, so a phosphatase has to remove the phosphate to reverse the regulation. There are four known groups:
- PP1
- PP2A
- PP2B (AKA calcineurin)
- PP2C
The first three have sequence homology in the catalytic domain, but differ in substrate specifity.
Ser/Thr-specific protein phosphatases are regulated by their location within the cell and by specific inhibitor proteins.