Distinct Roles for Two G –G Interfaces in Cell Polarity Control by a Yeast Heterotrimeric G Protein
نویسندگان
چکیده
Saccharomyces cerevisiae mating pheromones trigger dissociation of a heterotrimeric G protein (G ) into G guanosine triphosphate (GTP) and G . The G dimer regulates both mitogen-activated protein (MAP) kinase cascade signaling and cell polarization. Here, by independently activating the MAP kinase pathway, we studied the polarity role of G in isolation from its signaling role. MAP kinase signaling alone could induce cell asymmetry but not directional growth. Surprisingly, active G , either alone or with G -GTP, could not organize a persistent polarization axis. Instead, following pheromone gradients (chemotropism) or directional growth without pheromone gradients (de novo polarization) required an intact receptor–G module and GTP hydrolysis by G . Our results indicate that chemoattractantinduced cell polarization requires continuous receptor–G communication but not modulation of MAP kinase signaling. To explore regulation of G by G , we mutated G residues in two structurally distinct G –G binding interfaces. Polarity control was disrupted only by mutations in the N-terminal interface, and not the Switch interface. Incorporation of these mutations into a G –G fusion protein, which enforces subunit proximity, revealed that Switch interface dissociation regulates signaling, whereas the N-terminal interface may govern receptor–G coupling. These findings raise the possibility that the G heterotrimer can function in a partially dissociated state, tethered by the N-terminal interface.
منابع مشابه
Distinct Roles for Two G{alpha} G Interfaces in Cell Polarity Control by a Yeast Heterotrimeric G Protein
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