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Probing the mechanism of rhodopsin‐catalyzed transducin activation
Author(s) -
Natochin Michael,
Moussaif Mustapha,
Artemyev Nikolai O.
Publication year - 2001
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2001.00221.x
Subject(s) - transducin , rhodopsin , g protein , gtp' , conformational change , helix (gastropod) , biophysics , g protein coupled receptor , c terminus , protein subunit , gtp binding protein regulators , chemistry , n terminus , stereochemistry , biochemistry , biology , receptor , peptide sequence , amino acid , retinal , ecology , snail , gene , enzyme
An agonist‐bound G protein‐coupled receptor (GPCR) induces a GDP/GTP exchange on the G protein α‐subunit (Gα) followed by the release of GαGTP and Gβγ which, subsequently, activate their targets. The C‐terminal regions of Gα subunits constitute a major receptor recognition domain. In this study, we tested the hypothesis that the GPCR‐induced conformational change is communicated from the Gα C‐terminus, via the α5 helix, to the nucleotide‐binding β6/α5 loop causing GDP release. Mutants of the visual G protein, transducin, with a modified junction of the C‐terminus were generated and analyzed for interaction with photoexcited rhodopsin (R*). A flexible linker composed of five glycine residues or a rigid three‐turn α‐helical segment was inserted between the 11 C‐terminal residues and the α5 helix of Gα t ‐like chimeric Gα, Gα ti . The mutant Gα subunits with the Gly‐loop (Gα ti L) and the extended α5 helix (Gα ti H) retained intact interactions with Gβγ t , and displayed modestly reduced binding to R*. Gα ti H was capable of efficient activation by R*. In contrast, R* failed to activate Gα ti L, suggesting that the Gly‐loop absorbs a conformational change at the C‐terminus and blocks G protein activation. Our results provide evidence for the role of Gα C‐terminus/α5 helix/β6/α5 loop route as a dominant channel for transmission of the GPCR‐induced conformational change leading to G protein activation.