   3.6.5.1 | GTP + H2O = GDP + phosphate |
in the classic paradigm of G-protein signaling, GDP-bound Galpha remains associated with the non-dissociable betagamma subunits and, in combination with a G-protein coupled receptor (GPCR), represents the inactive state of the signaling pathway. Signal perception by GPCR facilitates the exchange of GTP for bound GDP on Galpha. The GTP-bound Galpha dissociates from the Gbetagamma dimer and both entities can interact with specific downstream effectors to transduce the signal. Galpha is restored to its GDP-bound conformation by its own intrinsic GTPase activity which leads to its reassociation with the Gbetagamma dimer and GPCR. The switch-like signaling mechanism has two distinct regulatory steps: the rate of GDP-GTP exchange facilitated by a cognate GPCR, which involves GDP release and GTP binding; and the rate of GTP hydrolysis by the Galpha protein |
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