The kelch proteins Gpb1 and Gpb2 inhibit Ras activity via association with the yeast RasGAP neurofibromin homologs Ira1 and Ira2.
The G protein-coupled receptor Gpr1 and associated Galpha subunit Gpa2 govern dimorphic transitions in response to extracellular nutrients by signaling coordinately with Ras to activate adenylyl cyclase in the yeast Saccharomyces cerevisiae. Gpa2 forms a protein complex with the kelch Gbeta mimic subunits Gpb1/2, and previous studies demonstrate that Gpb1/2 negatively control cAMP-PKA signaling via Gpa2 and an unknown second target. Here, we define these targets of Gpb1/2 as the yeast neurofibromin homologs Ira1 and Ira2, which function as GTPase activating proteins of Ras. Gpb1/2 bind to a conserved C-terminal domain of Ira1/2, and loss of Gpb1/2 results in a destabilization of Ira1 and Ira2, leading to elevated levels of Ras2-GTP and unbridled cAMP-PKA signaling. Because the Gpb1/2 binding domain on Ira1/2 is conserved in the human neurofibromin protein, an analogous signaling network may contribute to the neoplastic development of neurofibromatosis type 1.
Harashima
Toshiaki
T
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina 27710.
Anderson
Scott
S
The Scripps Research Institute, La Jolla, California 92037.
Yates
John R
JR
The Scripps Research Institute, La Jolla, California 92037.
Heitman
Joseph
J
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina 27710. Electronic address: heitm001@duke.edu.
D048868:Adaptor Proteins, Signal Transducing; D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases; D020690:GTPase-Activating Proteins; D017353:Gene Deletion; D006801:Humans; D009456:Neurofibromatosis 1 / Q000235:genetics / Q000378:metabolism; D025542:Neurofibromin 1 / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C476991:GPB1 protein, S cerevisiae; D020690:GTPase-Activating Proteins; C476990:Gpb2 protein, S cerevisiae; C065725:IRA1 protein, S cerevisiae; D025542:Neurofibromin 1; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; C489015:RAS2 protein, S cerevisiae; D018631:ras Proteins; D000262:Adenylyl Cyclases