GTPbound

GTP-bound refers to a molecular state in which a protein, typically a small GTPase, is bound to guanosine triphosphate (GTP). In this state the protein often adopts a conformation that enables interaction with specific effector proteins and downstream signaling or regulatory activities. The GDP-bound form is usually contrasted as the inactive state, though the exact functional dichotomy can vary among different GTPases.

For GTPases, binding of GTP induces conformational changes in regions known as switch I and switch II, which create surfaces for effector recognition. Hydrolysis of the bound GTP to GDP (often accelerated by GTPase-activating proteins, or GAPs) returns the protein to a low-affinity, inactive state and resets the cycle. Guanine nucleotide exchange factors (GEFs) promote the release of GDP and the binding of GTP, thereby reactivating the protein. Some regulators and chaperones further modulate localization and nucleotide cycling, contributing to spatial and temporal control of signaling.

Structurally, GTPases belong to the P-loop NTPase superfamily and share conserved motifs that coordinate the nucleotide and Mg2+. The presence of GTP rather than GDP stabilizes specific conformations that recruit downstream effectors, influence membrane association, or alter interactions with binding partners.

Examples of GTP-bound states include Ras family proteins in cell growth signaling, Rab family proteins in vesicle trafficking, and bacterial EF-Tu in translation. Dysregulation of GTP binding or hydrolysis can contribute to disease, notably when activating mutations lock a GTPase in the GTP-bound, signaling-active form.