Small GTPase

Small GTPase is a type of enzyme that can hydrolyze guanosine triphosphate (GTP) to guanosine diphosphate (GDP). They are a subfamily of the larger GTPase superfamily and are often referred to as 'molecular switches'. Small GTPases regulate a wide variety of processes in the cell, including growth, cellular differentiation, cell movement and lipid vesicle transport.

Function

Small GTPases function as binary switches, cycling between an inactive GDP-bound state and an active GTP-bound state. This cycle is regulated by Guanine nucleotide exchange factors (GEFs), GTPase-activating proteins (GAPs), and Guanosine nucleotide dissociation inhibitors (GDIs). GEFs facilitate the release of GDP to allow binding of GTP, GAPs increase the GTPase activity of the small GTPase, and GDIs inhibit the dissociation of GDP from the small GTPase.

Families

Small GTPases are grouped into five families, which are the Ras, Rho, Rab, Arf, and Ran families. Each family is characterized by a distinct set of regulators and effectors, and regulates a distinct set of cellular functions.

Ras

The Ras family is involved in transmitting signals within cells (cellular signal transduction). Mutations in Ras proteins can lead to the production of permanently activated proteins, resulting in oncogenic transformation.

Rho

The Rho family is known for its role in regulating the actin cytoskeleton, which is important for processes such as cell migration and cell division.

Rab

The Rab family is the largest family of small GTPases, and is involved in vesicle trafficking.

Arf

The Arf (ADP-ribosylation factor) family is also involved in vesicle trafficking, specifically in the formation of coated vesicles.

Ran

The Ran (RAs-related Nuclear protein) family is involved in the transport of RNA and proteins through the nuclear pore complex.

See also

• GTPase
• Guanine nucleotide exchange factors
• GTPase-activating proteins
• Guanosine nucleotide dissociation inhibitors