A monomeric G-protein (also known as small G protein or small GTPases, is the umbrella term for a family of signal transducing proteins. These comprise of: Rab, Arf, Ras, Ran and Rho, which are also vital in the growth of cells, as well as cell transport, motility, cytokinesis and cell differentiation. Monomeric G proteins comprise of three forms:
- an 'inactive' form in which the monomeric G-protein is bound to GDP (guanosine diphosphate), and
- In order to activate the inactive form of monomeric G-protein, a guanine exchange factor is needed.
- the 'active' form in which the Monomeric G-protein is bound to GTP (guanosine triphosphate).
Notably, monomeric G-proteins are small (ranging around 20-25 kDa) compared with larger types of G protein like heterotrimeric proteins (which are typically 30-35 kDa). To inactivate a monomeric G protein, a GTPase activating protein (GAP) is required to hydrolyse the GTP to GDP as they have weak intrinsic GTPase activity.