Phosphorylated Gβ is a directional cue during yeast gradient tracking

Abstract

Budding yeast cells interpret shallow pheromone gradients from cells of the opposite mating type, polarize their growth toward the pheromone source, and fuse at the chemotropic growth site. We previously proposed a deterministic, gradient-sensing model that explains how yeast cells switch from the intrinsically positioned default polarity site (DS) to the gradient-aligned chemotropic site (CS) at the plasma membrane. Because phosphorylation of the mating-specific Gβ subunit is thought to be important for this process, we developed a biosensor that bound to phosphorylated but not unphosphorylated Gβ and monitored its spatiotemporal dynamics to test key predictions of our gradient-sensing model. In mating cells, the biosensor colocalized with both Gβ and receptor reporters at the DS and then tracked with them to the CS. The biosensor concentrated on the leading side of the tracking Gβ and receptor peaks and was the first to arrive and stop tracking at the CS. Our data showed that the concentrated localization of phosphorylated Gβ correlated with the tracking direction and final position of the G protein and receptor, consistent with the idea that gradient-regulated phosphorylation and dephosphorylation of Gβ contributes to gradient sensing. Cells expressing a nonphosphorylatable mutant form of Gβ exhibited defects in gradient tracking, orientation toward mating partners, and mating efficiency.

Mechanism of commitment to a mating partner in Saccharomyces cerevisiae

“…, 1998 ; Choudhury et al. , 2018 ; Abdul-Ganiyu et al. , 2021 ), and the upstream MAPKK ( Errede and Ge, 1996 ), all of which appear to be adaptive pathways.…”

“…In addition to inducing BAR1 expression, MAPK activation induces expression of SST2, a regulator of G protein signaling (RGS) protein that inactivates Ga (Dohlman et al, 1996;Apanovitch et al, 1998), and MSG5, a phosphatase that dephosphorylates the MAPK (Doi et al, 1994;Chen and Thorner, 2007). MAPK also directly binds (Bhattacharyya et al, 2006) and phosphorylates (Repetto et al, 2018) the scaffold Ste5, both subunits of Gbg (Li et al, 1998;Choudhury et al, 2018;Abdul-Ganiyu et al, 2021), and the upstream MAPKK (Errede and Ge, 1996), all of which appear to be adaptive pathways. Other adaptive pathways may also be triggered by MAPK activation (Yu et al, 2008).…”

Mechanism of commitment to a mating partner in Saccharomyces cerevisiae

“…In addition to inducing BAR1 expression, MAPK activation induces expression of SST2 , a regulator of G protein signaling (RGS) protein that inactivates Gα (Dohlman et al, 1996; Apanovitch et al, 1998), and MSG5 , a phosphatase that dephosphorylates the MAPK (Doi et al, 1994; Chen and Thorner, 2007). MAPK also directly binds (Bhattacharyya et al, 2006) and phosphorylates (Repetto et al, 2018) the scaffold Ste5, both subunits of Gβγ (Li et al, 1998; Choudhury et al, 2018; Abdul-Ganiyu et al, 2021), and the upstream MAPKK (Errede and Ge, 1996), all of which appear to be adaptive pathways. Other adaptive pathways may also be triggered by MAPK activation (Yu et al, 2008).…”

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

“…3C). Of note, receptor phosphorylation by the kinases Yck1/2 is itself regulated: upon recruitment by activated Gα, Fus3 phosphorylates Gβ [35], which increases its affinity to Yck1/2, titrating the kinases away from the receptors and prolonging the active state [92] thus preserving pheromone signaling and ensuring efficient polarization and mating [93]. Regulation by RGS Sst2 is required for chemotropism [94], and is more complex than sole inhibition of Gα, as Sst2 also acts positively by promoting receptor retention at the plasma membrane [95].…”