Protein—Tyrosine Kinases and Their Substrates
Protein phosphorylation, through its ability to increase or decrease the activity of proteins, plays a central role in cellular regulation. Most proteins known to be regulated by phosphorylation are substrates for both a protein kinase and a protein phosphatase. Indeed, the ready reversibility of protein phosphorylation makes it ideally suited for rapid responses. Protein phosphorylation is used extensively in the internal cellular response pathways to external stimuli. Receptor-mediated recognition of hormones, growth factors, and neurotransmitters is commonly transduced across the plasma membrane through the activation of intracellular protein kinases. Many of the surface receptors for peptide mitogens are themselves membrane-spanning protein kinases consisting of an external ligand-binding domain and a cytoplasmic protein kinase domain (for review, see Yarden and Ullrich, 1988). The EGF, PDGF, and CSF-1 receptors are examples of this type. In these cases signal transduction is a direct result of activation of the receptor protein kinase upon binding of the growth factor.
KeywordsCatalytic Domain Tyrosine Phosphorylation Rous Sarcoma Virus Chicken Embryo Fibroblast Protein Kinase Domain
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