Receptor Protein Tyrosine Kinases and Phosphatases

Excerpt

There are many mechanisms for transducing signals across the plasma membrane via cell-surface receptors (see Table 1). Two of these directly involve protein phosphorylation in the sense that the cell-surface receptors in question have the intrinsic ability to catalyze protein phosphorylation or dephosphorylation (Fig. 1). In the first category are the receptor protein kinases, which display specificity for phosphorylating either tyrosine or serine residues in their targets. A large number of growth factor receptors are receptor protein tyrosine kinases (PTKs), and in these cases ligand binding leads to activation of a cytoplasmic catalytic domain and the consequent tyrosine phosphorylation of a series of target proteins, which propagate a cytoplasmic signal. Examples of this type of receptor are the epidermal growth factor (EGF), plasma-derived growth factor (PDGF), and insulin receptors. Receptor protein serine kinases have only recently been discovered. So far there is no direct evidence that ligand binding activates the...