Effects of Mg2+ and the βγ-subunit complex on the interactions of guanine nucleotides with G proteins

T. Higashijima, K. M. Ferguson, P. C. Sternweis

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Abstract

Mg2+ interacts with the α subunits of guanine nucleotide-binding regulatory proteins (G proteins) in the presence of guanosine-5'-[γ-thio]triphosphate (GTPγS) to form a highly fluorescent complex from which nucleotide dissociates very slowly. The apparent K(d) for interaction of G(α)·GTPγS with Mg2+ is approximately 5 nM, similar to the K(m) for G protein GTPase activity. G(βγ) increases the rate of dissociation of GTPγS from G(α)·GTPγS or G(α)·GTPγS·Mg2+ at low concentrations of Mg2+. When the concentration of Mg2+ exceeds 1 mM, G(βγ) dissociates from G(βγ)·G(α)·GTPγS·Mg2+. Compared with the dramatic effect of Mg2+ on binding of GTPγS to G(α), the metal has relatively little effect on the binding of GDP. However, G(βγ) increases the affinity of G(α) for GDP by more than 100-fold. High concentrations of Mg2+ promote the dissociation of GDP from G(βγ)·G(α)·GDP, apparently without causing subunit dissociation. The steady-state rate of GTP hydrolysis is strictly correlated with the rate of dissociation of GDP from G(α) under all conditions examined. Thus, there are at least two sites for interaction of Mg2+ with G protein-nucleotide complexes. Furthermore, binding of G(βγ) and GTPγS to G(α) is negatively cooperative, while the binding interaction between G(βγ) and GDP is strongly positive.

Original languageEnglish (US)
Pages (from-to)762-766
Number of pages5
JournalJournal of Biological Chemistry
Volume262
Issue number2
StatePublished - 1987

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Guanine Nucleotides
GTP-Binding Proteins
Carrier Proteins
Nucleotides
Proteins
Guanosine
GTP Phosphohydrolases
Guanosine Triphosphate
Hydrolysis
Metals

ASJC Scopus subject areas

  • Biochemistry

Cite this

Effects of Mg2+ and the βγ-subunit complex on the interactions of guanine nucleotides with G proteins. / Higashijima, T.; Ferguson, K. M.; Sternweis, P. C.

In: Journal of Biological Chemistry, Vol. 262, No. 2, 1987, p. 762-766.

Research output: Contribution to journalArticle

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