| Modification Notes |
Heterotrimeric G proteins function to relay information from cell surface receptors to intracellular effectors. Each of a very broad range of receptors specifically detects an extracellular stimulus (a photon, pheromone, odorant, hormone or neurotransmitter) while the effectors (i.e., adenyl cyclase), which act to generate one or more intracellular messengers, are less numerous. In mammals, G protein å, ∫ and © polypeptides are encoded by at least 16, 4 and 7 genes, respectively. Most interest in G proteins has been focused on their å subunits, since these proteins bind and hydrolyze GTP and most obviously regulate the activity of the best studied effectors. Four distinct classes of Gå subunits have been identified; these include Gå s, Gå i, Gå q and Gå 12/13. The two members of the fourth class of Gå subunit proteins, Gå 12 and Gå 13, are insensitive to ADP-ribosylation by pertussis toxin, share 67% identity with each other and less than 45% identity with other Gå subunits and are widely expressed in a broad range of tissues. Human Gå 12 may be phosphorylated at Ser 67. |