Signal perception and transduction: the role of protein kinases

Cells can react to environmental changes by transduction of extracellular s ignals, to produce intracellular responses. Membrane-impermeable signal mol ecules are recognized by receptors, which are localized on the plasma membr ane of the cell. Binding of a ligand can result in the stimulation of an in trinsic enzymatic activity of its receptor or the modulation of a transduci ng protein. The modulation of one or more intracellular transducing protein s can finally lead to the activation or inhibition of a so-called 'effector protein'. In many instances, this also results in altered gene expression. Phosphorylation by protein kinases is one of the most common and important regulatory mechanisms in signal transmission. This review discusses the no n-channel transmembrane receptors and their downstream signaling, with spec ial focus on the role of protein kinases. (C) 1999 Elsevier Science B.V. Al l rights reserved.