The G protein beta subunit is essential for multiple responses to chemoattractants in Dictyostelium.
Increasing evidence suggests that the beta gamma-subunit dimers of heterotrimeric G proteins play a pivotal role in transducing extracellular signals. The recent construction of G beta null mutants (g beta-) in Dictyostelium provides a unique opportunity to study the role of beta gamma dimers in signaling processes mediated by chemoattractant receptors. We have shown previously that g beta- cells fail to aggregate; in this study, we report the detailed characterization of these cells. The g beta- cells display normal motility but do not move towards chemattractants. The typical GTP-regulated high affinity chemoattractant-binding sites are lost in g beta- cells and membranes. The g beta- cells do not display chemoattractant-stimulated adenylyl cyclase or guanylyl cyclase activity. These results show that in vivo G beta links chemoattractant receptors to effectors and is therefore essential in many chemoattractant-mediated processes. In addition, we find that G beta is required for GTP gamma S stimulation of adenylyl cyclase activity, suggesting that the beta gamma-dimer activates the enzyme directly. Interestingly, the g beta- cells grow at the same rate as wild-type cells in axenic medium but grow more slowly on bacterial lawns and, therefore, may be defective in phagocytosis.
Wu
L
L
Department of Biological Chemistry, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA.
Valkema
R
R
Van Haastert
P J
PJ
Devreotes
P N
PN
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002465:Cell Movement; D002630:Chemotactic Factors / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D004023:Dictyostelium / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006162:Guanylate Cyclase / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D016296:Mutagenesis; D010587:Phagocytosis; D015398:Signal Transduction; D013997:Time Factors
D002630:Chemotactic Factors; D046911:Macromolecular Substances; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D006162:Guanylate Cyclase