GTP

Guanosine triphosphate (GTP) is a nucleotide composed of the guanine base, the ribose sugar, and three phosphate groups. As a high-energy phosphate donor, GTP participates in a variety of cellular reactions and can be interconverted with GDP and GMP through kinase and phosphatase activities. In cells, GTP serves as a substrate for RNA synthesis and as an energy source or cofactor in numerous processes beyond transcription.

In protein synthesis, GTP provides energy for several steps. During translation, elongation factors such as EF-Tu and EF-G hydrolyze GTP to drive the delivery and positioning of aminoacyl-tRNA on the ribosome and the translocation of tRNA and mRNA. GTP is also used during initiation and termination to regulate factor activity and ribosome dynamics.

GTPases constitute a large family of molecular switches that regulate signaling and cellular traffic. When bound to GTP, these proteins are in an active state; hydrolysis to GDP returns them to an inactive state. Examples include the Ras, Rab, Ran, and Rho families, which control processes such as vesicle trafficking, cytoskeletal organization, nuclear transport, and various signaling pathways.

GTP also influences microtubule dynamics. Tubulin binds GTP, and tubulin dimers add to growing microtubules in the GTP-bound form. Intra-microtubule GTP hydrolysis modulates stability and contributes to dynamic instability, a key feature of microtubule behavior.

Metabolically, GTP is generated from GDP by nucleoside diphosphate kinases and serves as a substrate for RNA polymerases. It is found in the cytosol and organelles, including mitochondria. Researchers use non-hydrolyzable analogs such as GTPγS to study GTPase activity and signaling.