Chloride Effects on G▪ Subunit Dissociation

• Published in: The Journal of biological chemistry Vol. 271; no. 15; pp. 8791 - 8795
• Main Authors: Toyoshige, Michihiro, Basi, Nirmal S., Rebois, R. Victor
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 12-04-1996; American Society for Biochemistry and Molecular Biology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.15.8791

The stimulatory guanine nucleotide binding protein (G▪) is heterotrimeric (αβ▪), and mediates activation of adenylyl cyclase by a ligand-receptor complex. The α subunit of G▪ (G▪α) has a guanine nucleotide binding site, and activation occurs when tightly bound GDP is displaced by GTP. Together, GDP and fluoroaluminate (AlF▪▪) form a transition state analog of GTP that activates G▪. The work of other investigators suggests that AlF▪▪ causes subunit dissociation when it activates G▪. We have observed that in solution AlF▪▪ did not cause G▪ subunits to dissociate unless NaCl was also present. The effect of NaCl was concentration dependent (10-200 mM). Omitting F▪, Al▪, or Mg▪ prevented the NaCl-induced dissociation of G▪ subunits. Na▪SO▪ could not substitute for NaCl in causing subunit dissociation, but KCl could, suggesting that the anion was responsible for the effect. G▪ subunit reassociation occurred when the concentration of Cl▪ was reduced even though the concentrations of AlF▪▪ and Mg▪ were maintained. The absence of Cl▪ did not prevent AlF▪▪ binding to G▪α. We have concluded that AlF▪▪, a ligand which is capable of activating G proteins, can bind to G▪ in solution without causing subunit dissociation.