Gβγ Isoforms Selectively Rescue Plasma Membrane Localization and Palmitoylation of Mutant Gα_s and Gα_q

Mutation of Gα_q or Gα_s N-terminal contact sites for Gβγ resulted in α subunits that failed to localize at the plasma membrane or undergo palmitoylation when expressed in HEK293 cells. We now show that overexpression of specific βγ subunits can recover plasma membrane localization and palmitoylation of the βγ-binding-deficient mutants of α_s or α _q. Thus, the βγ-binding-defective α is completely dependent on co-expression of exogenous βγ for proper membrane localization. In this report, we examined the ability of β_1-5 in combination with γ₂ or γ₃ to promote proper localization and palmitoylation of mutant α_s or α_q. Immunofluorescence localization, cellular fractionation, and palmitate labeling revealed distinct subtype-specific differences in βγ interactions with α subunits. These studies demonstrate that 1) α and βγ reciprocally promote the plasma membrane targeting of the other subunit; 2) β₅, when coexpressed with γ₂ or γ₃, fails to localize to the plasma membrane or promote plasma membrane localization of mutant α_s or α_q; 3) β₃ is deficient in promoting plasma membrane localization of mutant α_s and α_q, whereas β₄ is deficient in promoting plasma membrane localization of mutant α_q; 4) both palmitoylation and interactions with βγ are required for plasma membrane localization of α.