Yeast one-hybrid gγ recruitment system for identification of protein lipidation motifs

Let it stick: Strategies and applications for intracellular plasma membrane targeting of proteins in Saccharomyces cerevisiae

Lipid binding domains and protein lipidations are essential features to recruit proteins to intracellular membranes, enabling them to function at specific sites within the cell. Membrane association can also be exploited to answer fundamental and applied research questions, from obtaining insights into the understanding of lipid metabolism to employing them for metabolic engineering to redirect fluxes. This review presents a broad catalog of membrane binding strategies focusing on the plasma membrane of Saccharomyces cerevisiae. Both lipid binding domains (pleckstrin homology, discoidin-type C2, kinase associated-1, basic-rich and bacterial phosphoinositide-binding domains) and co- and post-translational lipidations (prenylation, myristoylation and palmitoylation) are introduced as tools to target the plasma membrane. To provide a toolset of membrane targeting modules, respective candidates that facilitate plasma membrane targeting are showcased including their in vitro and in vivo properties. The relevance and versatility of plasma membrane targeting modules are further highlighted by presenting a selected set of use cases.

Positive Detection of GPCR Antagonists Using a System for Inverted Expression of a Fluorescent Reporter Gene

The yeast Saccharomyces cerevisiae is a useful eukaryotic host organism for studying GPCRs as monomolecular models. Fluorescent reporter gene assays for GPCRs provide a convenient assay for measuring receptor activity using fluorometric instruments. Generally, these assays detect receptor activation by agonistic ligands as the induction of fluorescent reporter expression, whereas antagonistic activities are detected by competition with agonistic ligands, resulting in decreases in fluorescence intensity. In the current study, we established a system for inverted expression of a fluorescent reporter by incorporating a PEST-tag and finding out a promoter inhibited by activation of the GPCR signaling pathway from yeast endogenous promoters. Because agonists prevent fluorescent reporter expression in this system, antagonists compete with agonists and yield increased fluorescence intensity. We used the yeast endogenous pheromone receptor as a model GPCR to demonstrate the feasibility of our system for positive detection targeted at antagonists. Compared to results when only agonists were added to yeast cells, more than 10-fold higher fluorescence intensity was observed when antagonists were added in combination with agonists. The approach described here has the potential to markedly accelerate the identification of GPCR antagonists by providing rapid and straightforward responses.

Continuous crossbreeding of sake yeasts using growth selection systems for a-type and α-type cells

Sake yeasts belong to the budding yeast species Saccharomyces cerevisiae and have high fermentation activity and ethanol production. Although the traditional crossbreeding of sake yeasts is a time-consuming and inefficient process due to the low sporulation rates and spore viability of these strains, considerable effort has been devoted to the development of hybrid strains with superior brewing characteristics. In the present work, we describe a growth selection system for a- and α-type cells aimed at the crossbreeding of industrial yeasts, and performed hybridizations with sake yeast strains Kyokai No. 6, No. 7 and No. 9 to examine the feasibility of this approach. We successfully generated both a- and α-type strains from all parental strains, and acquired six types of hybrids by outcrossing. One of these hybrid strains was subjected to continuous crossbreeding, yielding the multi-hybrid strain, which inherited the genetic characteristics of Kyokai No. 6, No. 7 and No. 9. Notably, because all of the genetic modifications of the yeast cells were introduced using plasmids, these traits can be easily removed. The approach described here has the potential to markedly accelerate the crossbreeding of industrial yeast strains with desirable properties.

Rapid evaluation of tyrosine kinase activity of membrane-integrated human epidermal growth factor receptor using the yeast Gγ recruitment system

Epidermal growth factor receptor (EGFR) is a member of the receptor tyrosine kinase family and plays key roles in the regulation of fundamental cellular processes, including cell proliferation, migration, differentiation, and survival. Deregulation of EGFR tyrosine kinase activity is involved in the development and progression of human cancers. In the present study, we attempted to develop a method to evaluate the tyrosine kinase activity of human EGFR using the yeast Gγ recruitment system. Autophosphorylation of tyrosine residues on the cytoplasmic tail of EGFR induces recruitment of Grb2-fused Gγ subunits to the inner leaflet of the plasma membrane in yeast cells, which leads to G-protein signal transduction and activation of downstream signaling events, including mating and diploid cell growth. We demonstrate that our system is applicable for the evaluation of tyrosine kinase inhibitors, which are regarded as promising drug candidates to prevent the growth of tumor cells. This approach provides a rapid and easy-to-use tool to select EGFR-targeting tyrosine kinase inhibitors that are able to permeate eukaryotic membranes and function in intracellular environments.