G protein coupled receptor agonists and antagonists and methods of activating and inhibiting G protein coupled receptors using the same

1. A chimeric polypeptide comprising:

a) a first domain comprising a first intracellular loop (i1 loop) or a fragment thereof of a G protein coupled receptor (GPCR), wherein said GPCR is a Class A or Class B GPCR, and

b) a second domain, attached to the first domain, wherein said second domain comprises a cell-penetrating, membrane-tethering hydrophobic moiety comprising a lipid, a cholesterol, or a steroid;

wherein said chimeric polypeptide is an agonist or antagonist of the GPCR,

wherein said first domain does not comprise a native extracellular portion of said GPCR and wherein said i1 loop fragment comprises at least 5 contiguous amino acid residues of the first intracellular loop.

2. The chimeric polypeptide of claim 1 , wherein said second domain is attached at the N-terminal end of said first domain.

3. The chimeric polypeptide of claim 1 , wherein said second domain comprises a hydrophobic moiety that is selected from the group consisting of a: capryloyl (C 8 ); nonanoyl(C 9 ); capryl(C 10 ); undecanoyl(C 11 ); lauroyl(C 12 ); tridecanoyl(C 13 ); myristoyl(C 14 ); pentadecanoyl(C 15 ); palmitoyl (C 16 ); phytanoyl ((CH 3 ) 4 ); heptadecanoyl(C 17 ); stearoyl(C 18 ); nonadecanoyl(C 19 ); arachidoyl(C 20 ); heniecosanoyl(C 21 ); behenoyl(C 22 ); trucisanoyl(C 23 ); and lignoceroyl(C 24 ) moiety.

4. The chimeric polypeptide of claim 3 , wherein said second domain comprises a palmitoyl moiety.

5. The chimeric polypeptide of claim 1 , wherein said i1 loop fragment comprises at least 7 contiguous amino acid residues of the first intracellular loop.

6. The chimeric polypeptide of claim 1 , wherein said GPCR is a protease-activated receptor (PAR).

7. The chimeric polypeptide of claim 6 , wherein the protease-activated receptor is selected from the group consisting of PAR1, PAR2, and PAR4.

8. The chimeric polypeptide of claim 1 , wherein the G-protein coupled receptor is selected from the group consisting of a luteinizing hormone receptor, a follicle stimulating hormone receptor, a thyroid stimulating hormone receptor, a calcitonin receptor, a glucagon receptor, a glucagon-like peptide 1 receptor (GLP-1), a metabotropic glutamate receptor, a secretin receptor, a growth hormone releasing factor (GRF) receptor, a protease-activated receptor (PAR), a cholecystokinin receptor, a somatostatin receptor, a melanocortin receptor, an Adenosine Diphosphate (ADP) receptor, an adenosine receptor, a thromboxane receptor, a platelet activating factor receptor, an adrenergic receptor, a 5-HT receptor, CXCR4, CCR5, a chemokine receptor, a neuropeptide receptor, an opioid receptor, a parathyroid hormone (PTH) receptor, and a vasoactive intestinal peptide (VIP) receptor.

9. A pharmaceutical composition comprising the chimeric polypeptide of claim 1 and a pharmaceutically acceptable carrier.

10. The chimeric polypeptide of claim 1 , wherein the said G-protein coupled receptor is selected from the group consisting of Cholecystokinin A (CCKA) receptor, Cholecystokinin B (CCKB) receptor, Somatostatin Receptor Subtype 2 (SSTR2), and Substance P (SubP) receptor.

11. The chimeric polypeptide of claim 1 , wherein said second domain comprises a steroid.

12. The chimeric polypeptide of claim 1 , wherein said second domain comprises a lipid moiety.

13. The chimeric polypeptide of claim 1 , wherein said GPCR is a chemokine receptor.

14. The chimeric polypeptide of claim 13 , wherein said chemokine receptor is CXCR4 or CCR5.

15. The chimeric polypeptide of claim 1 , wherein said GPCR is a Class A GPCR.

16. The chimeric polypeptide of claim 1 , wherein said GPCR is a Class B GPCR.

17. The chimeric polypeptide of claim 1 , wherein the second domain is attached at the C-terminal end of the first domain.

18. The chimeric polypeptide of claim 1 , wherein the second domain comprises a myristoyl(C 14 ) or pentadecanoyl(C 15 ) moiety.

19. The chimeric polypeptide of claim 1 , wherein the second domain comprises a cholesterol.

20. A kit comprising (1) a pharmaceutical composition comprising a chimeric polypeptide and a pharmaceutically acceptable carrier, (2) a container, pack, or dispenser, and (3) instructions for administration, wherein said chimeric polypeptide comprises:

a) a first domain comprising a first intracellular loop (i1 loop) or a fragment thereof of a G protein coupled receptor (GPCR), wherein said GPCR is a Class A or Class B GPCR, and

b) a second domain, attached to the first domain, wherein said second domain comprises a cell-penetrating, membrane-tethering hydrophobic moiety comprising a lipid, a cholesterol, a phospholipid, a steroid, a sphingosine, a ceramide, an octyl-glycine, a 2-cyclohexylalanine, or a benzolylphenylalanine;

wherein said chimeric polypeptide is an agonist or antagonist of the GPCR,

wherein said first domain does not comprise a native extracellular portion of said GPCR and wherein said i1 loop fragment comprises at least 5 contiguous amino acid residues of the first intracellular loop.

21. The kit of claim 20 , wherein said second domain of the chimeric polypeptide comprises a lipid moiety.

22. The kit of claim 20 , wherein the second domain comprises a palmitoyl(C 16 ), myristoyl(C 14 ), or pentadecanoyl(C 15 ) moiety.

23. The kit of claim 20 , wherein the second domain comprises a cholesterol.

24. A chimeric polypeptide comprising:

a) a first domain comprising an isolated i1loop or fragment thereof of a protease-activated receptor (PAR), and

b) a second domain, attached to the first domain, wherein said second domain comprises a palmitoyl;

wherein said chimeric polypeptide is an agonist or antagonist of said PAR,

wherein said first domain does not comprise a native extracellular portion of said PAR and wherein said i1 loop fragment comprises at least 5 contiguous amino acid residues of the first intracellular loop.

25. A chimeric polypeptide comprising:

a) a first domain comprising a first intracellular loop (i1 loop) or a fragment thereof of a G protein coupled receptor (GPCR), wherein said GPCR is a Class A or Class B GPCR, and

b) a second domain, attached to the first domain, wherein said second domain comprises a cell-penetrating, membrane-tethering hydrophobic moiety selected from the group consisting of a phospholipid, a sphingosine, a ceramide, an octyl-glycine, a 2-cyclohexylalanine, and a benzolylphenylalanine,

wherein said chimeric polypeptide is an agonist or antagonist of the GPCR,

wherein said first domain does not comprise a native extracellular portion of said GPCR and wherein said i1 loop fragment comprises at least 5 contiguous amino acid residues of the first intracellular loop.