Ggamma in dictyostelium: its role in localization of gbetagamma to the membrane is required for chemotaxis in shallow gradients.
G-protein-mediated signal transduction pathways play an essential role in the developmental program of the simple eukaryotic organism Dictyostelium discoideum. Database searches have yielded 11 Galpha-subunits, a single Gbeta-subunit, but no Ggamma-subunits. We report here the purification, cDNA isolation, and functional analysis of a Ggamma-subunit. Like Gbeta, the Ggamma appears to be unique and hybridization studies show that Ggamma and Gbeta are expressed in parallel during development. Species-wide sequence comparisons of Ggamma-subunits and gamma-like domains of RGS proteins reveal short stretches of highly conserved residues as well as the common CXXL motif at the COOH-terminal of Ggammas that target Gbetagammas to plasma membrane. Overexpression of a CSVL-deleted Ggamma (GgammaDelta) in wild-type cells shifts Gbetagamma to the cytosol and selectively impairs certain G-protein-mediated signal transduction pathways. These cells are able to respond to increments in the stimulus, but are unable to sense chemoattractant gradients. They neither move directionally nor recruit PH-domains to their leading edge. Thus, a full complement of membrane-tethered Gbetagamma is required for sensing shallow gradients, but is not essential for responses to increments in extracellular stimuli.
Zhang
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N
Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Long
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Y
Devreotes
P N
PN
D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002449:Cell Aggregation / Q000502:physiology; D002630:Chemotactic Factors / Q000502:physiology; D002633:Chemotaxis / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics* / Q000302:isolation & purification; D004023:Dictyostelium / Q000235:genetics*; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D020710:RGS Proteins / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics; D017385:Sequence Homology; D015398:Signal Transduction / Q000502:physiology
D002630:Chemotactic Factors; D018076:DNA, Complementary; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D008565:Membrane Proteins; D020710:RGS Proteins; D020962:Heterotrimeric GTP-Binding Proteins