The C-terminus of the G protein α subunit controls the affinity of nucleotides

Naoki Kimata, Takahiro Yamashita, Take Matsuyama, Yasushi Imamoto, Yoshinori Shichida*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

The C-terminus of the G protein α subunit has a well-known role in determining the selective coupling with the cognate G protein-coupled receptor (GPCR). In fact, rhodopsin, a prototypical GPCR, exhibits active state [metarhodopsin II (MII)] stabilization by interacting with G protein [extra formation of MII (eMII)], and the extent of stabilization is affected by the C-terminal sequence of Gα. Here we examine the relationship between the amount of eMII and the activation efficiency of Gi mutants whose Giα forms have different lengths of the C-terminal sequence of Goα. The results show that both the activation efficiencies of Gi and the amounts of eMII were affected by mutations; however, there was no correlation between them. This finding suggested that the C-terminal region of Gα not only stabilizes MII (active state) but also affects the nucleotide-binding site of Gα. Therefore, we measured the activation efficiency of these mutants by MII at several concentrations of GDP and GTP and calculated the rate constants of GDP release, GDP uptake, and GTP uptake. These rate constants of the Gi mutants were substantially different from those of the wild type, indicating that the replacement of the amino acid residues in the C-terminus alters the affinity of nucleotides. The rate constants of GDP uptake and GTP uptake showed a strong correlation, suggesting that the C-terminus of Giα controls the accessibility of the nucleotide-binding site. Therefore, our results strongly suggest that there is a long-range interlink between the C-terminus of Giα and its nucleotide-binding site.

Original languageEnglish
Pages (from-to)2768-2774
Number of pages7
JournalBiochemistry
Volume51
Issue number13
DOIs
Publication statusPublished - 2012 Apr 3
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry

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