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Mechanism of G‐protein Activation by Rhodopsin †
Author(s) -
Shichida Yoshinori,
Morizumi Takefumi
Publication year - 2007
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2006-03-22-ir-854
Subject(s) - rhodopsin , transducin , chromophore , chemistry , schiff base , g protein coupled receptor , g protein , protein subunit , retinal , gtp' , g alpha subunit , stereochemistry , biophysics , signal transduction , biochemistry , photochemistry , biology , enzyme , gene
Rhodopsin is a member of the family of G‐protein‐coupled receptors (GPCRs), and is an excellent molecular switch for converting light signals into electrical response of the rod photoreceptor cells. Light initiates cis – trans isomerization of the retinal chromophore of rhodopsin and leads to the formation of several thermolabile intermediates during the bleaching process. Recent investigations have identified spectrally distinguishable two intermediate states that can interact with the retinal G‐protein, transducin, and have elucidated the functional sharing of these intermediates. The initial contact with GDP‐bound G‐protein occurs in the meta‐Ib intermediate state, which has a protonated Schiff base as its chromophore. The meta‐Ib intermediate in the complex with the G‐protein converts to the meta‐II intermediate with releasing GDP from the α‐subunit of the G protein. Meta‐II has a de‐protonated Schiff base chromophore and induces binding of GTP to the α‐subunit of the G‐protein. Thus, the GDP–GTP exchange reaction, namely G‐protein activation, by rhodopsin proceeds through at least two steps, with conformational changes in both rhodopsin and the G‐protein.