Small GTPase

In biology, small GTPases are small (20-25 kDa) proteins that bind to guanosine triphosphate (GTP). This family of proteins is homologous to Ras GTPases and also called the Ras superfamily GTPases. Together with heterotrimeric G-proteins they constitute the G-proteins. They are all GTPases and share common features, but small GTPases have slightly different structures and mechanisms of action.

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Small GTPases regulate a wide variety of processes in the cell, including growth, cellular differentiation, cell movement and lipid vesicle transport.

The Ras superfamily

There are more than a hundred proteins in the Ras superfamily. Based on structure, sequence and function, the Ras superfamily is divided into eight main families, each of which is further divided into subfamilies: Ras, Rho, Rab, Rap, Arf, Ran, Rheb, Rad and Rit.

Each subfamily shares the common core G domain, which provides essential GTPase and nucleotide exchange activity.

The surrounding sequence helps determine the functional specificity of the small GTPase, for example the 'Insert Loop', common to the Rho subfamily, specifically contributes to binding to effector proteins such as IQGAP and WASP.

See also

• GTP-binding protein regulators