GTPázis

GTPázis, or GTPases, are a diverse family of enzymes that catalyze the hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP) and inorganic phosphate. They function as molecular switches in a wide range of cellular processes, being active when bound to GTP and inactive when bound to GDP. The switch between these states is driven by regulatory proteins that promote GDP release and GTP binding, and by factors that enhance GTP hydrolysis.

Most GTPases fall into two broad groups: small GTPases, which are typically around 20 to 25 kilodaltons, and larger GTPases that participate in specialized activities. Well-known small GTPases include the Ras, Rho, Rab, Ran, and Arf families. Key examples of larger GTPases include dynamin, involved in membrane fission, and tubulin, a structural GTPase essential for microtubule dynamics. The activity of many GTPases is tightly controlled by accessory regulators: guanine nucleotide exchange factors (GEFs) promote the exchange of GDP for GTP to activate the GTPase, GTPase-activating proteins (GAPs) accelerate GTP hydrolysis to inactivate it, and GDP-dissociation inhibitors (GDIs) regulate the cycling of certain small GTPases, such as Rab, by keeping them in the cytosol and modulating their membrane association.

Functions of GTPases are central to signaling pathways, vesicle trafficking, cytoskeleton organization, nucleocytoplasmic transport, organelle dynamics, and protein synthesis. Dysregulation or mutation of GTPases, particularly Ras family members, is linked to cancer and other diseases, making them important subjects of research and therapeutic interest. Structurally, GTPases share a conserved GTP-binding domain with motifs that coordinate nucleotide binding and hydrolysis, and undergo conformational changes in their switch regions that determine effector interactions.