Expression of functional human olfactory cyclic nucleotide gated (CNG) channel in recombinant host cells and use thereof in cell based assays to identify GPCR modulators
The present invention relates to isolated nucleic acid sequences that encode human olfactory cyclic nucleotide gated (CNG) channel subunits, and the corresponding polypeptides. The invention further relates to the use of human CNG channels to profile, screen for, and identify compounds that modulate the human olfactory CNG channel. More specifically, the invention relates to the expression of the human olfactory CNG channel in cells, preferably mammalian cells, and the use of these cells in high throughput cell-based assays to identify compounds that enhance or block human olfactory CNG function. Compounds that activate the olfactory CNG channel will enhance smell and can be used to make foods more palatable for individuals with attenuated olfactory function. Conversely, compounds that inhibit the olfactory CNG channel will inhibit smell and can be use to block malodors. Additionally, the invention relates to the use of cell-based olfactory CNG channel assays to identify modulates of G-protein coupled receptor (GPCRs) and other proteins that regulate cyclic nucleotide levels.
1. A eukaryotic host cell which has been genetically engineered by the introduction of three olfactory channel subunit encoding nucleic acid sequences which upon expression result in a heteromeric olfactory cyclic nucleotide gated (CNG) channel and further by the introduction of a nucleic acid sequence encoding an exogenous G protein coupled receptor wherein said heteromeric olfactory CNG channel is comprised of (i) a OCNC1 olfactory channel subunit polypeptide which exhibits at least 99% sequence identity to the polypeptide of SEQ. ID NO: 9 or 12; (ii) a OCNC2 olfactory channel subunit polypeptide which exhibits at least 99% sequence identity to the polypeptide of SEQ. ID NO: 10 and (iii) a β1b olfactory CNG channel subunit polypeptide which exhibits at least 99% sequence identity to the polypeptide of SEQ. ID NO: 11.
2. The eukaryotic cell of claim 1 which is a mammalian cell.
3. The eukaryotic cell of claim 2 which is a human cell.
4. The mammalian cell of claim 2 which is selected from the group consisting of a human embryonic kidney cell, COS cell, African green monkey kidney cell, mouse L cell , L+K cell and BHK cell.
5. The mammalian cell of claim 2 which is selected from a HEK293, MDCK, HEK, HEK293T, BHK, COS; NIH 3T3, SWISS 3T3 and CHO cell.
6. The eukaryotic cell of claim 1 wherein said OCNC1 polypeptide, OCNC2 polypeptide and β1b polypeptide respectively have the polypeptide sequences of SEQ. ID NO: 9, SEQ. ID NO: 10 and SEQ. ID NO: 11 respectively.
7. The eukaryotic cell of claim 1 wherein said heteromeric olfactory CNG channel comprises at least one substitution mutation relative to SEQ ID NO:9, SEQ. ID NO: 10, SEQ. ID NO: 11 or SEQ ID NO:12.
8. The eukaryotic cell of claim 7 wherein said substitution mutation is selected from the change of a cysteine to a tryptophan at the position corresponding to 1735 in the OCNC1 polypeptide of SEQ. ID NO: 9 and/or a mutation at the positions corresponding to 1741 and 1742 in the OCNC1 polypeptide of SEQ ID NO:9 resulting in the change in a glutamate to a methionine in the polypeptide of SEQ. ID NO:9.
9. The eukaryotic cell of claim 1 wherein said olfactory CNG OCNC1 subunit polypeptide, OCNC2 subunit polypeptide and β1b subunit polypeptide respectively comprise the polypeptide sequences contained in SEQ. ID NO: 12, SEQ. ID NO:10 and SEQ. ID NO: 11.
10. The eukaryotic cell of claim 1 wherein the G protein coupled receptor is stably expressed.
11. The eukaryotic cell of claim 1 wherein the G protein coupled receptor is an olfactory receptor.
12. The eukaryotic cell of claim 1 wherein the olfactory receptor is mOREG.
13. The eukaryotic cell of claim 1 which is a HEK-293 cell.
14. The eukaryotic cell of claim 1 which is loaded with a membrane potential dye that permits changes in fuorescence to be detected.
15. The eukaryotic cell of claim 14 wherein said membrane potential dye is selected from the group consisting of Molecular Devices Membrane Potential Kit (cat#R8034), Di-4-ANEPPS (Pyridinium, 4-(2-(6(dibutylamino)-2naphthalenyl)ethenyl)-1-(3-sulfopropyl))-, hydroxide, inner salt), DiSBACC4(2)(bis-(1,2-dibarbituric acid)-trimethine oxanol), DiSBAC4(3) (bis?(1,3-dibarbituric acid)-trimethine oxanol), CC-2-DMPE (Pacific Blue™ 1,2-dietradecanoyl-sn-glycerol-3-phosphoethanolmine, triethylammonium salt) and SBFI-AM (1,3-Benzenedicarboxylic acid, 4,4′-[1,4,10-trioxa 7, 13-diazacyclopentadecane-7, 13-diylbis(5-methoxy-6, 12-benzofurandiyl)lbis-, tettrakis[(acetyloxy)Methyl] ester; (Molecular Probes).
16. The eukaryotic cell of claim 14 wherein said dye is a calcium-sensitive or sodium-sensitive fuorescent dye.
17. An assay for identifying a compound that modulates olfactory CNG channel activity which comprises contacting a eukaryotic cell according to claim 1 with a putative modulator of CNG channel activity and identifying whether said compound modulates CNG channel activity by detecting changes in intracellular ion concentrations.
18. The assay of claim 17 wherein said intracellular ion is calcium or sodium.
19. The assay of claim 18 wherein changes in intracellular calcium or sodium ions are detected using a calcium or sodium-sensitive fuorescent dye.
20. The assay of claim 18 wherein changes in intracellular ion concentrations are detected fluorimetrically.
21. The assay of claim 20 wherein a fuorescence plate reader is used to measure changes in fluorescence.
22. The assay of claim 20 wherein a voltage imaging plate reader is used to measure changes in fuorescence.
23. The assay of claim 17 which is used to identify compounds that modulate said G protein coupled receptor.
24. The assay of claim 23 wherein said G protein coupled receptor is an olfactory receptor.
25. The assay of claim 24 wherein said olfactory receptor is mOREG.