Answer: Transducting the signal from an activated receptor to the next protein in the pathway.
Explanation:
G-proteins are a family of proteins whose main function is to carry a signal from a receptor on the cell membrane to one or more target proteins. So, G-proteins are very important in signal transduction. They depend on the nucleotide guanosine triphosphate (GTP) for activation.
They are the third largest family of proteins in eukaryotic cells and hundreds have been described. G-proteins are involved in signal transduction in many different ways, which is why there are so many different types of these proteins. They can be involved in signalling the activation or silencing of DNA translation, in the reception of hormonal and neuronal signals, etc. They are characterized by their interaction with guanosine triphosphate (GTP) leading to hydrolysis of the nucleotide to guanosine diphosphate (GDP). In this way, a stimulus from outside the cell, a ligand for example, accesses the cell's receptor associated with G-protein or GPCR, triggering a cascade of enzymatic activities or second messengers in response. Therefore, GTPase activity is crucial for their functioning as biological switches.
G-protein-coupled receptors (GPCR) comprise the targets of several biogenic amines, eicosanoids, and other molecules that send signals to target cells such as lipids, hormonal peptides, opiates, amino acids (GABA), and many other protein peptides and ligands. Effectors that are regulated by G-protein include enzymes such as adenyl cyclase, phospholipase C, phosphodiesterases and plasma membrane ion channels selective for Ca²+ and K+.
Also, because of their number and physiological importance, GPCRs are widely used targets for drugs.
