Membrane trafficking of heterotrimeric G proteins via the endoplasmic reticulum and Golgi.
Membrane targeting of G-protein alphabetagamma heterotrimers was investigated in live cells by use of Galpha and Ggamma subunits tagged with spectral mutants of green fluorescent protein. Unlike Ras proteins, Gbetagamma contains a single targeting signal, the CAAX motif, which directed the dimer to the endoplasmic reticulum. Endomembrane localization of farnesylated Ggamma(1), but not geranylgeranylated Ggamma(2), required carboxyl methylation. Targeting of the heterotrimer to the plasma membrane (PM) required coexpression of all three subunits, combining the CAAX motif of Ggamma with the fatty acyl modifications of Galpha. Galpha associated with Gbetagamma on the Golgi and palmitoylation of Galpha was required for translocation of the heterotrimer to the PM. Thus, two separate signals, analogous to the dual-signal targeting mechanism of Ras proteins, cooperate to target heterotrimeric G proteins to the PM via the endomembrane.
Michaelson
David
D
Department of Medicine, Cell Biology and Pharmacology, NYU School of Medicine, 10016, USA.
Ahearn
Ian
I
Bergo
Martin
M
Young
Stephen
S
Philips
Mark
M
D020816:Amino Acid Motifs; D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017368:Protein Prenylation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction
D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins