An NMR-based identification of a peptide fragment from the β-subunit of a G-protein showing specific interactions with the GBB domain of the Ste20 kinase in budding yeast

In mitogen-activated protein kinase (MAPK) cascades of budding yeast, pheromone-induced mating signal is transmitted by interactions between the β-subunit of a G-protein (G-β) and the G-β binding (GBB) domain of Ste20 kinase. Previously, mutational analyses of the β-subunit of G-protein had identified two critical mutations which abrogate binding of the GBB domain of Ste20. In this work, we have identified, by use of NMR spectroscopy, a peptide fragment from the G-β that shows specific interactions with the isolated GBB domain of Ste20. A model structure of the Ste20/G-β complex reveals that the interface of the hetero-complex may be sustained by parallel orientation of two potentially interacting helical segments that are further stabilized by ionic, hydrogen bond, and helix macro-dipole interactions.