Protein Tyrosine Phosphatases

The reversible covalent modification of proteins by the addition and removal of a phosphate group is an important theme in signal transduction in mammalian cells. There is a large superfamily of protein kinases that catalyse the addition of a phosphate group to hydroxyl residues on the side chains of the amino acids serine, threonine, or tyrosine. Similarly there is a large family of protein phosphatases that catalyze the removal of phosphate groups from phosphoserine, phosphothreonine, and phosphotyrosine residues. A dynamic interplay between protein kinases and protein phosphatases exists in vivo whereby the phosphorylation status of the target protein is determined by the opposing actions of these kinases and phosphatases.