[NMR paper] The mechanism of aluminum-independent G-protein activation by fluoride and magnesium.

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The mechanism of aluminum-independent G-protein activation by fluoride and magnesium. 31P NMR spectroscopy and fluorescence kinetic studies.

Related Articles The mechanism of aluminum-independent G-protein activation by fluoride and magnesium. 31P NMR spectroscopy and fluorescence kinetic studies.

J Biol Chem. 1993 Feb 5;268(4):2393-402

Authors: Antonny B, Sukumar M, Bigay J, Chabre M, Higashijima T

With magnesium present, fluoride and aluminum ions activate heterotrimeric G-proteins by forming AlFx complexes that mimic the gamma phosphate of a GTP. We report compelling evidence for a newly proposed process of G-protein activation by fluoride and magnesium, without Al3+. With millimolar Mg2+ and F-, Gs and Gt activate adenylylcyclase and cGMP-phosphodiesterase, respectively. In 31P NMR, addition of magnesium to Gi1 alpha GDP or Gt alpha GDP solutions containing fluoride, but no Al3+, modifies the chemical shift of the GDP beta phosphorus, suggesting that magnesium interacts with the beta phosphate. Titration of this effect indicates that two Mg2+ are bound per G alpha. Biphasic activation kinetics, monitored by G alpha tryptophan fluorescence, suggests the rapid binding of one Mg2+ to G alpha GDP and the slow association of another Mg2+, in correlation with fluoride binding and G alpha activation. The deactivation rate upon fluoride dilution shows a second order dependence with respect to the residual F- concentration, suggesting the sequential release of at least three F-/G alpha. Thus, in millimolar Mg2+ and F-, and without Al3+, two Mg2+ and three F- bind sequentially to G alpha GDP and induce the switch to an active G alpha (GDP-MgF3)Mg state, which is structurally analogous to G alpha (GDP-AlFx)Mg and to G alpha (GTP)Mg.

PMID: 8381408 [PubMed - indexed for MEDLINE]



Source: PubMed