1a0r
HETEROTRIMERIC COMPLEX OF PHOSDUCIN/TRANSDUCIN BETA-GAMMAHETEROTRIMERIC COMPLEX OF PHOSDUCIN/TRANSDUCIN BETA-GAMMA
Structural highlights
FunctionGBB1_BOVIN Guanine nucleotide-binding proteins (G proteins) are involved as a modulator or transducer in various transmembrane signaling systems. The beta and gamma chains are required for the GTPase activity, for replacement of GDP by GTP, and for G protein-effector interaction. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBACKGROUND: Phosducin binds tightly to the beta gamma subunits (Gt beta gamma) of the heterotrimeric G protein transducin, preventing Gt beta gamma reassociation with Gt alpha-GDP and thereby inhibiting the G-protein cycle. Phosducin-like proteins appear to be widely distributed and may play important roles in regulating many heterotrimeric G-protein signaling pathways. RESULTS: The 2.8 A crystal structure of a complex of bovine retinal phosducin with Gt beta gamma shows how the two domains of phosducin cover one side and the top of the seven-bladed beta propeller of Gt beta gamma. The binding of phosducin induces a distinct structural change in the beta propeller of Gt beta gamma, such that a small cavity opens up between blades 6 and 7. Electron density in this cavity has been assigned to the farnesyl moiety of the gamma subunit. CONCLUSIONS: beta gamma subunits of heterotrimeric G proteins can exist in two distinct conformations. In the R (relaxed) state, corresponding to the structure of the free beta gamma or the structure of beta gamma in the alpha beta gamma heterotrimer, the hydrophobic farnesyl moiety of the gamma subunit is exposed, thereby mediating membrane association. In the T (tense) state, as observed in the phosducin-Gt beta gamma structure, the farnesyl moiety of the gamma subunit is effectively buried in the cavity formed between blades 6 and 7 of the beta subunit. Binding of phosducin to Gt beta gamma induces the formation of this cavity, resulting in a switch from the R to the T conformation. This sequesters beta gamma from the membrane to the cytosol and turns off the signal-transduction cascade. Regulation of this membrane association/dissociation switch of Gt beta gamma by phosducin may be a general mechanism for attenuation of G protein coupled signal transduction cascades. Phosducin induces a structural change in transducin beta gamma.,Loew A, Ho YK, Blundell T, Bax B Structure. 1998 Aug 15;6(8):1007-19. PMID:9739091[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences |
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