GTP-binding proteins, or G proteins, constitute a superfamily capable of binding GTP or GDP. G proteins are activated by binding GTP and are inactivated by hydrolyzing GTP to GDP. This general mechanism enables G proteins to perform a wide range of biologic activities.[supplied by OMIM, Jan 2003] see less GTP-binding proteins, or G proteins, constitute a superfamily capable of binding GTP or GDP. G proteins are activated by binding GTP and are inactivated by hydrolyzing GTP to GDP. This general mechanism enables G proteins to perform a wide range of biologic activities.[supplied by OMIM, Jan 2003]