MOLECULAR-BIOLOGY OF SIGNAL-TRANSDUCING G-PROTEINS

Living cells possess the remarkable ability to discriminate among the enormous variety of chemical and physical stimuli that they receive. G proteins are a central component of the molecular machinery that allows cells to respond appropriately to each of these stimuli. G proteins are molecular switches whose properties of guanine nucleotide binding and hydrolysis are eminently suited to perform the transduction of external signals into intracellular effects. Molecular analysis shows that the components of signalling pathway-receptors and effectors linked by G proteins as well as the subunits of G proteins, are members of families of structurally diverse proteins. This diversity of molecules helps in processing the variety of signals a cell senses. But it is unclear how both specificity and cross-regulation of signalling pathways are achieved in the same cell with high fidelity.