Identification of Gα₁₁ as the phospholipase C-activating G-protein of turkey erythrocytes

A 43 kDa phospholipase C-activating protein has been purified previously from turkey erythrocytes and shown to express immunological properties expected of that of the G(q) family of G-protein α-subunits [Waldo, Boyer, Morris and Harden (1991) J. Biol. Chem. 266, 14217-14225]. Internal amino acid sequence has now been obtained from this protein which shares 50-100 % sequence identity with sequences encoded by mammalian Gα₁₁ and Gα(q) cDNAs. To identify the purified protein unambiguously, it was necessary to compare its amino acid sequence with the sequence encoded by avian G-protein α-subunit cDNA. As such, mouse Gα(q) was used as a probe to screen turkey brain and fetal-turkey blood cDNA libraries. A full-length cDNA was identified that encodes avian Gα₁₁, on the basis of its 96-98 % amino acid identity with mammalian Gα(π). All eight peptides sequenced from the turkey erythrocyte phospholipase C-activating protein are completely contained within the deduced amino acid sequence of the avian Gα(11) cDNA. Expression of this cDNA in Sf9 cells by using a baculovirus expression system resulted in the production of a 43 kDa protein that reacts strongly with antisera to the G(q) family of G-protein α-subunits and activated purified avian phospholipase C in an AlF^-₄-dependent manner. Taken together, these results unambiguously identify the protein purified from turkey erythrocytes, on the basis of its capacity to activate avian phospholipase C, as Gα(π).