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Roles of the Transducin α-Subunit α4-Helix/α4-β6 Loop in the Receptor and Effector Interactions
Journal article   Open access   Peer reviewed

Roles of the Transducin α-Subunit α4-Helix/α4-β6 Loop in the Receptor and Effector Interactions

Michael Natochin, Alexey E Granovsky, Khakim G Muradov and Nikolai O Artemyev
The Journal of biological chemistry, Vol.274(12), pp.7865-7869
03/19/1999
DOI: 10.1074/jbc.274.12.7865
url
https://doi.org/10.1074/jbc.274.12.7865View
Published (Version of record) Open Access

Abstract

The visual GTP-binding protein, transducin, couples light-activated rhodopsin (R*) with the effector enzyme, cGMP phosphodiesterase in vertebrate photoreceptor cells. The region corresponding to the α4-helix and α4-β6 loop of the transducin α-subunit (Gtα) has been implicated in interactions with the receptor and the effector. Ala-scanning mutagenesis of the α4-β6 region has been carried out to elucidate residues critical for the functions of transducin. The mutational analysis supports the role of the α4-β6 loop in the R*-Gtα interface and suggests that the Gtα residues Arg310 and Asp311 are involved in the interaction with R*. These residues are likely to contribute to the specificity of the R* recognition. Contrary to the evidence previously obtained with synthetic peptides of Gtα, our data indicate that none of the α4-β6 residues directly or significantly participate in the interaction with and activation of phosphodiesterase. However, Ile299, Phe303, and Leu306 form a network of interactions with the α3-helix of Gtα, which is critical for the ability of Gtα to undergo an activational conformational change. Thereby, Ile299, Phe303, and Leu306play only an indirect role in the effector function of Gtα.

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