Improved identification of agonist-mediated Gαi-specific human G-protein-coupled receptor signaling in yeast cells by flow cytometry

Comparative analyses of site-directed mutagenesis of human melatonin MTNR1A and MTNR1B receptors using a yeast fluorescent biosensor

Melatonin is an indoleamine neurohormone made by the pineal gland. Its receptors, MTNR1A and MTNR1B, are members of the G-protein-coupled receptor (GPCR) family and are involved in sleep, circadian rhythm, and mood disorders, and in the inhibition of cancer growth. These receptors, therefore, represent significant molecular targets for insomnia, circadian sleep disorders, and cancer. The yeast Saccharomyces cerevisiae is an attractive host for assaying agonistic activity for human GPCR. We previously constructed a GPCR-based biosensor employing a high-sensitivity yeast strain that incorporated both a chimeric yeast-human Gα protein and a bright fluorescent reporter gene (ZsGreen). Similar approaches have been used for simple and convenient measurements of various GPCR activities. In the current study, we constructed a fluorescence-based yeast biosensor for monitoring the signaling activation of human melatonin receptors. We used this system to analyze point mutations, including previously unreported mutations of the consensus sequences of MTNR1A and MTNR1B melatonin receptors and compared their effects. Most mutations in the consensus sequences significantly affected the signaling capacities of both receptors, but several mutations showed differences between these subtype receptors. Thus, this yeast biosensor holds promise for revealing the functions of melatonin receptors.

The mapping of yeast's G-protein coupled receptor with an atomic force microscope

An atomic force microscope (AFM) can measure the adhesion force between a sample and a cantilever while simultaneously applying a rupture force during the imaging of a sample. An AFM should be useful in targeting specific proteins on a cell surface. The present study proposes the use of an AFM to measure the adhesion force between targeting receptors and their ligands, and to map the targeting receptors. In this study, Ste2p, one of the G protein-coupled receptors (GPCRs), was chosen as the target receptor. The specific force between Ste2p on a yeast cell surface and a cantilever modified with its ligand, α-factor, was measured and found to be approximately 250 pN. In addition, through continuous measuring of the cell surface, a mapping of the receptors on the cell surface could be performed, which indicated the differences in the Ste2p expression levels. Therefore, the proposed AFM system is accurate for cell diagnosis.

Construction of a yeast-based signaling biosensor for human angiotensin II type 1 receptor via functional coupling between Asn295-mutated receptor and Gpa1/Gi3 chimeric Gα

Angiotensin II (Ang II) type 1 receptor (AGTR1) is a G-protein-coupled receptor (GPCR). Its natural ligand, Ang II, is an important effector molecule controlling blood pressure and volume in the cardiovascular system, and is consequently involved in various diseases such as hypertension and heart failure. Thus, the signaling mediator, AGTR1, is a significant molecular target in medicinal and therapeutic fields. Yeast is a useful organism for sensing GPCR signaling because it provides a simplified version of the complicated machinery used by mammalian cells for signal transduction. Although yeast cells can successfully transmit a signal through a variety of human GPCRs expressed in the cell membrane, there have been no reports of the functional activation of AGTR1-mediated signaling in yeast cells. In the present study, we introduced a single mutation into human AGTR1 and used yeast-human chimeric Gα to exert the functional activation of AGTR1 in yeast cells. The engineered yeast cells expressing AGTR1 mutated at Asn295 and the chimeric Gα successfully transmitted the signal inside the yeast cells in response to Ang II peptide and its analogs (Ang III and Ang IV peptides) added to the assay medium. Further, we demonstrated that the autocrine Ang II peptide and its analog, produced and secreted by the engineered yeast cells, could by themselves promote AGTR1-mediated signaling. This means that screening for agonistic peptides with various sequences from a self-produced genetic library would be a viable strategy. Thus, the constructed yeast biosensor, integrating an Asn295-mutated AGTR1 receptor, will be valuable in the design of drugs to treat AGTR1-related diseases.

Bright fluorescence monitoring system utilizing Zoanthus sp. green fluorescent protein (ZsGreen) for human G-protein-coupled receptor signaling in microbial yeast cells

G-protein-coupled receptors (GPCRs) are currently the most important pharmaceutical targets for drug discovery because they regulate a wide variety of physiological processes. Consequently, simple and convenient detection systems for ligands that regulate the function of GPCR have attracted attention as powerful tools for new drug development. We previously developed a yeast-based fluorescence reporter ligand detection system using flow cytometry. However, using this conventional detection system, fluorescence from a cell expressing GFP and responding to a ligand is weak, making detection of these cells by fluorescence microscopy difficult. We here report improvements to the conventional yeast fluorescence reporter assay system resulting in the development of a new highly-sensitive fluorescence reporter assay system with extremely bright fluorescence and high signal-to-noise (S/N) ratio. This new system allowed the easy detection of GPCR signaling in yeast using fluorescence microscopy. Somatostatin receptor and neurotensin receptor (implicated in Alzheimer's disease and Parkinson's disease, respectively) were chosen as human GPCR(s). The facile detection of binding to these receptors by cognate peptide ligands was demonstrated. In addition, we established a highly sensitive ligand detection system using yeast cell surface display technology that is applicable to peptide screening, and demonstrate that the display of various peptide analogs of neurotensin can activate signaling through the neurotensin receptor in yeast cells. Our system could be useful for identifying lead peptides with agonistic activity towards targeted human GPCR(s).