Brain G protein gamma subunits contain an all-trans-geranylgeranylcysteine methyl ester at their carboxyl termini.

Abstract

We have shown previously that guanine nucleotide-binding protein (G protein) beta gamma complexes purified from bovine brain membranes are methyl esterified on a C-terminal cysteine residue of the gamma polypeptide. In the present study, 3H-methylated G beta gamma complexes cleaved to their constituent amino acids by exhaustive proteolysis were shown to contain radiolabeled material that coeluted with geranylgeranylcysteine methyl ester on reversed-phase HPLC and two TLC systems. Further treatment by performic acid oxidation yielded radiolabeled material that coeluted with L-cysteic acid methyl ester, verifying that the prenyl modification occurs on a C-terminal cysteine residue. Analysis by gas chromatography-coupled mass spectrometry of material released from purified G beta gamma by treatment with Raney nickel positively identified the covalently bound lipid as an all-trans-geranylgeranyl (C20) isoprenoid moiety. To delineate the distribution of this modification among gamma subunits, purified G beta gamma complexes were separated into 5-kDa (gamma 5) and 6-kDa (gamma 6) forms of the gamma polypeptide by reversed-phase HPLC. Gas chromatography-coupled mass spectrometry analyses of Raney nickel-treated purified gamma 5 and gamma 6 subunits showed that both polypeptides were modified by geranylgeranylation. These results demonstrate that at least two forms of brain gamma subunit are posttranslationally modified by geranylgeranylation and carboxyl methylation. These modifications may be important for targeting G beta gamma complexes to membranes.

G protein βγ complex translocation from plasma membrane to Golgi complex is influenced by receptor γ subunit interaction

“…First, we examined whether the prenyl moiety that is post-translationally added to the γ subunit is the main determinant of the differential translocation. γ5 is geranylgeranylated and γ11 is farnesylated [17,18]. A farnesylated γ5 subunit mutant translocated more rapidly compared to the wild type γ5 but slower than the γ11 subunit.…”

A CAAX or a CAAL motif and a second signal are sufficient for plasma membrane targeting of ras proteins

“…Certain other CAAX containing proteins, including the ras-related proteins Krev 1/rap lA (Kawata et al, 1990;Buss et al, 1991) and G25K (Maltese and Sheridan, 1990), and the -y-subunits of brain G-proteins (Yamane et al, 1990;Mumby et al, 1990) have been shown to be geranylgeranylated. The CAAX motifs of these C20 modified proteins all terminate with a leucine residue indicating that the X amino acid determines whether a CAAX motif is a substrate for a farnesyl or geranylgeranyl transferase (Seabra et al, 1991;Finegold et al, 1991).…”

Effects of lovastatin on adenylyl cyclase activity and G proteins in GH4C1 cells

“…Although none of the G-protein subunits contain regions that might obviously associate with a lipid bilayer, the heterotrimer is bound to the plasma membrane due in part to the fact that the 7/-subunits are prenylated [5][6][7][8]. The carboxyl-terminal posttranslational modifications of G-protein 7~-subunits are important determinants of the subcellular location of the G-subunits.…”

“…Retinal 71 and brain ;g2 proteins have been shown to contain farnesyl [5,6] and geranylgeranyl [7,8] modifications in the C-terminal cysteine residues, respectively. On the other hand, the G~ proteins of the G i subfamily are myristoylated [9] and members of the Gs and Gq subfamilies of ~ units are palmitoylated [10,11].…”