Immunological detection of G-protein alpha-subunits in Dictyostelium discoideum

Putative G-protein alpha-subunits in Dictyostelium discoideum were detected on western blots using the antiserum A-569, raised against a peptide whose sequence is found in alpha-subunits of all known GTP-binding signal transducing proteins. Two bands with a MW of 40 kDa and 52 kDa were specifically recognized by the common peptide antiserum; the staining of both bands was strongly reduced when the antiserum was preincubated with the peptide that was used for antibody production. D.discoideum mutant HC213 (fgd A) lacks staining of the 40 kDa band, while the 52 kDa band is still present. This mutant is severely defective in cAMP receptor-G-protein interaction. We concluded that the primitive eukaryote D.discoideum contains proteins which show functional and physical similarity with the alpha-subunits of vertebrate G-proteins.