Small GTPase

From Wikipedia, the free encyclopedia

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

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

[edit] 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.