The Gα Subunit Signals through the Ste50 Protein during the Mating Pheromone Response in the Yeast Kluyveromyces lactis

Abstract

Yeast mating signal transduction pathways require a heterotrimeric G protein composed of G␣, G␤, and G␥ subunits connected to a mitogen-activated protein kinase (MAPK) module. While in Saccharomyces cerevisiae elimination of G␣ induces constitutive activation of the mating pathway, in Kluyveromyces lactis it produces partial sterility, which indicates that K. lactis G␣ (KlG␣) is required to positively activate mating. We use physical interaction experiments to determine that KlG␣ interacts with the adaptor protein KlSte50p. The Ras association (RA) domain of KlSte50p favored interaction with the GDP-bound KlG␣ subunit, and when the KlG␣ protein is constitutively activated, the interaction drops significantly. Additionally, KlSte50p strongly associates with the MAPK kinase kinase (MAPKKK) KlSte11p through its sterile alpha motif (SAM) domain.

A focus on yeast mating: From pheromone signaling to cell-cell fusion

“…Similarly, the Cryptococcus neoformans Ste50 homologue, which lacks a Ste5 homologue [56], is required for pheromone signaling and binds to the MAPKKK [57]. The Kluyveromyces lactis Ste50 homologue also binds the MAPKKK, as well as the Gα [58], suggesting that in S. pombe Ste4 may translate Gpa1 activation to the MAPKKK Byr2. Byr2 activation also requires the Ras1 GTPase, which is activated by a mating-specific GEF Ste6, itself under control of Ste11 transcription.…”

Mate and fuse: how yeast cells do it

“…Ste4 (not to be confused with its S. cerevisiae homonym) shows homology to budding yeast Ste50 [77], a protein involved in the activation of the MAPKKK Ste11 in S. cerevisiae [80]. Interestingly, a Ste50 homologue binds both MAPKKK and the Gα protein in K. lactis , an ascomycete closely related to S. cerevisiae [81], and is necessary for mating signalling in Cryptococcus neoformans , a basidiomycere species that lacks a Ste5 homologue [49,82], thus supporting the idea that Ste4 may link Gα with the MAPKKK Byr2.…”

Yeast on the milky way: genetics, physiology and biotechnology of Kluyveromyces lactis

“…They signal to a trimeric G protein with conserved α ‐, ß ‐ and γ ‐subunits. In contrast to S. cerevisiae , not only does the ßγ complex function in signalling but the G α subunit, albeit not essential, enhances mating efficiency and interacts with the adaptor protein Ste50 (Sanchez‐Paredes et al ., ). The central MAPK module, consisting of the MAPKKK Ste11, the MAPKK Ste7 and the MAPK Fus3, including the scaffold protein Ste5, is also conserved in K. lactis .…”

“…The pheromone pathway (Coria et al, 2006) and the cell wall integrity pathway (Backhaus et al, 2011) have been reviewed. See text for further details and references mating efficiency and interacts with the adaptor protein Ste50 (Sanchez-Paredes et al, 2011). The central MAPK module, consisting of the MAPKKK Ste11, the MAPKK Ste7 and the MAPK Fus3, including the scaffold protein Ste5, is also conserved in K. lactis.…”