In biology,<unk> s are<unk>  (20-25 kDa) proteins that bind to guanosine triphosphate (GTP).  This family of proteins is homologous to Ras<unk> s and also called the Ras superfamily<unk> s. Together with heterotrimeric G-proteins they constitute the G-proteins. They are all<unk> s and share common features, but<unk> s have slightly different structures and mechanisms of action.
A typical G-protein is active when bound to GTP and inactive when bound to GDP (i.e. when the GTP is hydrolyzed to GDP). The GDP can be then replaced by free GTP. Therefore, a G-protein can be switched on and off. GTP hydrolysis is accelerated by<unk>  accelating proteins (GAPs), while GTP exchange is catalyzed by Guanine nucleotide exchange factors (GEFs). Activation of a GEF typically activates its cognate G-protein, while activation of a GAP results in inactivation of the cognate G-protein.<unk> s regulate a wide variety of processes in the cell, including growth, cellular differentiation, cell movement and lipid vesicle transport.
Small GTPase
Calmodulin
Rho GTPase
Disintegrin
Caspase
Neutron moderator
GTPase activating protein
Transmembrane protein