(a) Functional cell-based assay using authentic exendin-4 (Ex4). sequence. The result suggests that our system could facilitate the discovery of functional peptide ligands of GPCRs. or expression. Subsequently, we investigated whether the culture supernatants of Ex lover4-secreting yeast cells could activate the hGLP1R of hGLP1R/LacZ-293 and hGLP1R/NLuc-293 cell lines. We cultured the cell lines with or without the culture supernatants of Ex lover4-secretory yeast (yeast-Ex4) or wild-type (WT) yeast (yeast-WT) and we observed significant reporter signals in both lines (Fig.?2b). Even though signal-noise ratio of hGLP1R/LacZ-293 was lower than that of hGLP1R/NLuc-293, we concluded that hGLP1R/LacZ-293 could be used as a fluorescent reporter collection for hGLP1R, because luciferase imaging has two drawbacks. First, we cannot detect luminescence if secreted luciferases run out of a limited amount of substrates in droplets. Second, the rate of photon production by luciferase is very low, hence luciferase imaging is not appropriate for high-throughput analysis. Open in a separate window Physique 2 Functional cell-based assay for evaluating the reporter cell lines. (a) Functional cell-based assay using authentic exendin-4 (Ex lover4). hGLP1R/NLuc-293 and hGLP1R/LacZ-293 were cultured in DMEM media with or without 30? nM authentic Ex4. WT HEK293 was used as a control. Values are mean??SD (n?=?3). Two-tailed Students with or without enterokinase reactions to the hGLP1R/NLuc-293 cells, and observed a significant increase in luminescence only when the peptides were cleaved by enterokinase (Fig.?6a). The result indicated that WT Ex lover4 produced by is usually functional and a free N-terminal was vital for the activation of GLP1R. The amounts of the purified WT Ex lover4 and Ex lover4 variants produced by were then quantified using liquid chromatography coupled to mass spectrometry, and their activities were evaluated using the hGLP1R/NLuc-293 cells. The Ex lover4 variants produced by experienced an activation capacity higher or comparable to that of WT Ex lover4 produced by (Fig.?6b). Though we did not obtain a variant with an at least 2-fold increased activity compared to Ex lover4, this is probably because Ex lover4 is usually a very strong agonist which was isolated from your venome of the Gila monster31, and we think it is advantageous that we succeeded in improving the activity of such a strong agonist. Open in a separate window Physique 6 Functional evaluation of Exendin-4 (Ex lover4) variants produced by (a) The functional assay using WT Ex lover4 produced by generating WT Ex lover4 fused with a FLAG sequence Tlr4 at the N-terminal ((as a host for generating peptides, we exhibited that the activities of the recognized Ex lover4 variants were not influenced by post-translational modifications or differences in Piperidolate hydrochloride secretion efficiencies (Fig.?6b). A previous study revealed that this hydrogen bonding of Glu387 of GLP1R and histidine at the N-terminus of the ligand is vital for the activity of GLP1R32. In the present study, functional peptides contained Ser (Fig.?6b, peptide 1) or Piperidolate hydrochloride Thr (Fig.?6b, peptide 4) at the N-terminus, suggesting that this amino acids were selected due to hydrogen bonding with hGLP1R. It is considered that further improvement of the throughput will be necessary Piperidolate hydrochloride to comprehensive characterization of the peptides mutation space. To improve the throughput, there is a method for increasing the generation velocity of droplets36 and methods of increasing the proportions of droplets made up of cells29,37. In addition, fluorescence-activated cell sorting on a microfluidics will improve the throughput to retrieve fluorescence-positive droplets. In conclusion, we exhibited that functional assay of hGLP1R could be performed by temporarily co-culturing the reporter mammalian cells and the yeast cells in a bulk assay. In addition, we encapsulated the mammalian cells and yeast cells in water-in-oil droplets using a droplet microfluidic device for high-throughput identification of peptide ligands against hGLP1R. We recognized novel functional ligands, one of which exhibited higher activity than that of Ex lover4 (Fig.?6b, peptide 2). The result suggested that this droplet assay system constructed in the present study could be effective in the identification of novel peptide ligands. In future studies, we will optimize our system to improve encapsulation efficiency and throughput by combining fluorescence-activated sorting and next-generation sequencers. Methods Construction of reporter cells To construct a reporter cell collection that constitutively produces human GLP1R (hGLP1R) and inducibily secretes NanoLuc in response to the.