S combinations, the sets of GPCR dimers are almost entirely unknown and thus their dominant roles are still poorly understood. Techniques to observe the dimerization of GPCRs include atomic force microscopy, electrophoresis, co-immunoprecipitation, cross-linkage, and fluorescence and bioluminescence resonance energy transfer (FRET and BRET) [3,4,6]. The FRET and BRET approaches are especially helpful for in vivo analysis and therefore are widely used for the studies of dimerized GPCRs. However, although the FRET and BRET techniques permit the direct monitoring of GPCR dimerization, it might be difficult touse these techniques to achieve rapid and facile identification of dimerizable candidates among numerous GPCR combinations. To overcome this limitation, here we established a specialized method to screen candidate heterodimer partners for target GPCRs based on the split-ubiquitin membrane yeast two-hybrid method. In addition, since our system is independent from the activation of mitogen-activated protein kinase (MAPK) signal, it permits not only the identification of heterodimer partners, but also the monitoring of ligand-induced conformational changes.Results and DiscussionWhile the original split-ubiquitin system enables comprehensive screening of protein-protein interactions [7], it is intrinsically possible that the addition of ligand triggers activation of pheromone ML 281 signaling via endogenous yeast heterotrimeric Gprotein [8]. The activation of pheromone signaling in yeast induces cell cycle arrest in G1 phase and triggers global changes in transcription of mating-related genes [9]. The ligand-induced G1 arrest that is exposed as robust growth inhibition in yeast cells [10] might lead to an inadequate assessment of reporter gene activity. Therefore, we constructed a yeast deletion mutant lacking the STE20 or STE11 gene involved in the activation of the MAPK cascade by using NMY51 as the parental strain with an aim to enable screening of GPCR dimers with and without ligand (Fig.Screening of Human GPCR Heterodimerand Table 1). Halo bioassays responding to a-factor pheromone showed the formations of a thin halo and no halos with 100 mg of a-factor in NMY61 (ste20D) and NMY62 (ste11D) yeast strains, respectively, revealing that ste11D allele provides more strict avoidance 23148522 of signal-promoted growth arrest in the presence of ligand (Fig. 2A). For checking the expressions of reporter genes, the growth assays in the presence of ligand were carried out (Fig. 2B). While the strains harboring mock vectors pBT3-C and pPR3-C were used as negative controls, those harboring pCCWAlg5 and pAI-Alg5 to express Alg5-NubI and Alg5-Cub-LexAVP16 were used as positive controls. Alg5-NubI is a yeast membrane protein fused with a WT Nub tag. The NubI tag interacts spontaneously with any Cub tag-containing constructs [11,12]. The deletion mutants (ste20D and ste11D) avoided the robust growth inhibition and therefore could allow the growth assays with ADE2 and HIS3 reporter genes even in the presence of ligand (Fig. 2B). We used the MAPK-defective NMY62 yeast strain for the following experiments. To test the viability of split-ubiquitin ased reporter gene assays for PS 1145 detecting GPCR dimers, we first analyzed the homodimerization of endogenous yeast pheromone receptor (Ste2p) in theFigure 1. Schematic illustration of yeast pheromone signaling pathway and principle for GPCR dimerization assay based on split-ubiquitin system in yeast. Agonistic ligand binding to t.S combinations, the sets of GPCR dimers are almost entirely unknown and thus their dominant roles are still poorly understood. Techniques to observe the dimerization of GPCRs include atomic force microscopy, electrophoresis, co-immunoprecipitation, cross-linkage, and fluorescence and bioluminescence resonance energy transfer (FRET and BRET) [3,4,6]. The FRET and BRET approaches are especially helpful for in vivo analysis and therefore are widely used for the studies of dimerized GPCRs. However, although the FRET and BRET techniques permit the direct monitoring of GPCR dimerization, it might be difficult touse these techniques to achieve rapid and facile identification of dimerizable candidates among numerous GPCR combinations. To overcome this limitation, here we established a specialized method to screen candidate heterodimer partners for target GPCRs based on the split-ubiquitin membrane yeast two-hybrid method. In addition, since our system is independent from the activation of mitogen-activated protein kinase (MAPK) signal, it permits not only the identification of heterodimer partners, but also the monitoring of ligand-induced conformational changes.Results and DiscussionWhile the original split-ubiquitin system enables comprehensive screening of protein-protein interactions [7], it is intrinsically possible that the addition of ligand triggers activation of pheromone signaling via endogenous yeast heterotrimeric Gprotein [8]. The activation of pheromone signaling in yeast induces cell cycle arrest in G1 phase and triggers global changes in transcription of mating-related genes [9]. The ligand-induced G1 arrest that is exposed as robust growth inhibition in yeast cells [10] might lead to an inadequate assessment of reporter gene activity. Therefore, we constructed a yeast deletion mutant lacking the STE20 or STE11 gene involved in the activation of the MAPK cascade by using NMY51 as the parental strain with an aim to enable screening of GPCR dimers with and without ligand (Fig.Screening of Human GPCR Heterodimerand Table 1). Halo bioassays responding to a-factor pheromone showed the formations of a thin halo and no halos with 100 mg of a-factor in NMY61 (ste20D) and NMY62 (ste11D) yeast strains, respectively, revealing that ste11D allele provides more strict avoidance 23148522 of signal-promoted growth arrest in the presence of ligand (Fig. 2A). For checking the expressions of reporter genes, the growth assays in the presence of ligand were carried out (Fig. 2B). While the strains harboring mock vectors pBT3-C and pPR3-C were used as negative controls, those harboring pCCWAlg5 and pAI-Alg5 to express Alg5-NubI and Alg5-Cub-LexAVP16 were used as positive controls. Alg5-NubI is a yeast membrane protein fused with a WT Nub tag. The NubI tag interacts spontaneously with any Cub tag-containing constructs [11,12]. The deletion mutants (ste20D and ste11D) avoided the robust growth inhibition and therefore could allow the growth assays with ADE2 and HIS3 reporter genes even in the presence of ligand (Fig. 2B). We used the MAPK-defective NMY62 yeast strain for the following experiments. To test the viability of split-ubiquitin ased reporter gene assays for detecting GPCR dimers, we first analyzed the homodimerization of endogenous yeast pheromone receptor (Ste2p) in theFigure 1. Schematic illustration of yeast pheromone signaling pathway and principle for GPCR dimerization assay based on split-ubiquitin system in yeast. Agonistic ligand binding to t.
