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

1. A polypeptide comprising:

a) a first domain comprising a third intracellular loop (i3 loop), or a fragment thereof of a G protein coupled receptor (GPCR), and

b) a second domain, attached to the first domain, wherein said second domain is a naturally or non-naturally occurring cell-penetrating, membrane-tethering moiety, wherein said polypeptide is a GPCR agonist or antagonist and does not comprise an extracellular portion of the GPCR and said first domain is at least 3 contiguous amino acid residues.

2. The polypeptide of claim 1 , wherein said first domain comprises at least 5 contiguous amino acid residues of the third intracellular loop.

3. The polypeptide of claim 1 , wherein said first domain comprises at least 7 contiguous amino acid residues of the third intracellular loop.

4. The polypeptide of claim 1 , wherein the first domain comprises 7 to 24 contiguous amino acid residues of the third intracellular loop.

5. The polypeptide of claim 1 , wherein the cell-penetrating, membrane-tethering moiety is hydrophobic.

6. The polypeptide of claim 1 , wherein the cell-penetrating, membrane-tethering moiety is non-peptidic.

7. The polypeptide of claim 6 , wherein the moiety comprises a lipid.

8. The polypeptide of claim 6 , wherein the moiety is selected from the group consisting of cholesterol, phospholipid, steroid, sphingosine, ceramide, octyl-glycine, 2-cyclohexylalanine, benzolylphenylalanine, and fatty acid.

9. The polypeptide of claim 8 , wherein the fatty acid moiety is selected from the group consisting of a 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 (methyl substituted C 16 ), heptadecanoyl (C 17 ), stearoyl (C 18 ), nonadecanoyl (C 19 ), arachidoyl (C 20 ), heniecosanoyl (C 21 ), behenoyl (C 22 ), trucisanoyl (C 23 ), and a lignoceroyl (C 24 ) group.

10. The polypeptide of claim 9 , wherein the fatty acid moiety is the palmitoyl or myristoyl group.

11. The polypeptide of claim 1 , wherein said fragment comprises one or more peptide bonds that have been replaced with a covalent bond which is not susceptible to cleavage by peptidases.

12. The polypeptide of claim 1 , wherein said GPCR 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 parathyroid hormone receptor, a vasoactive intestinal peptide receptor, a secretin receptor, a growth hormone releasing factor (GRF) receptor, protease-activated receptors (PARs), cholecystokinin receptors, somatostatin receptors, melanocortin receptors, ADP receptors, adenosine receptors, thromboxane receptors, platelet activating factor receptor, adrenergic receptors, 5-HT receptors, chemokine receptors, neuropeptide receptors, opioid receptors, parathyroid hormone (PTH) receptor, and vasoactive intestinal peptide (VIP) receptor.

13. The polypeptide of claim 12 , wherein the GPCR is selected from CCR5 or CXCR4.

14. The polypeptide of claim 1 , wherein said GPCR is selected from the group consisting of a protease-activated receptor (PAR), a peptide receptor, a chemokine receptor, and a nucleotide receptor.

15. The polypeptide of claim 14 , wherein said GPCR is selected from the group consisting of a PAR1, PAR2, PAR3, and a PAR4 receptor.

16. The polypeptide of claim 1 , wherein said first domain comprises an i3 loop or fragment thereof of a protease-activated receptor and said second domain is a lipid.

17. The polypeptide of claim 1 , wherein the second domain of the polypeptide further comprises 1-15 contiguous amino acid residues of a naturally-occurring transmembrane helix region of the GPCR immediately adjacent to the intracellular fragment.

18. The polypeptide of claim 1 , wherein the second domain of said polypeptide further comprises at least 1-7 contiguous amino acid residues of a transmembrane helix region of the GPCR.

19. The polypeptide of claim 1 , wherein the cell-penetrating, membrane-tethering moiety is attached to an N-terminal amino acid residue of said first domain.

20. The polypeptide of claim 1 , wherein said first domain comprises an amino acid sequence selected from the group consisting of SEQ ID NOS:1-16, 19-23, 29, and 33-36.

21. The polypeptide of claim 20 , wherein said first domain comprises a sequence selected from the group consisting of SEQ ID NO: 1-10 and 23.

22. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 1.

23. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 2.

24. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 3.

25. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 4.

26. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 5.

27. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 6.

28. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 7.

29. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 8.

30. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 9.

31. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 10.

32. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 11.

33. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 12.

34. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 13.

35. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 14.

36. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 15.

37. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 16.

38. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 19.

39. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 20.

40. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 21.

41. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 22.

42. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 23.

43. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 29.

44. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 33.

45. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 34.

46. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 35.

47. The polypeptide of claim 20 , wherein said first domain comprises the amino acid sequence of SEQ ID NO: 36.

48. The polypeptide of claim 20 , wherein said cell-penetrating, membrane-tethering moiety is a palmitoyl group.

49. The polypeptide of claim 20 , wherein said cell-penetrating, membrane-tethering moiety is a myristoyl group.

50. The polypeptide of claim 1 , wherein said cell-penetrating, membrane-tethering moiety comprises the amino acid sequence YCYVSII (SEQ ID NO: 40).

51. The polypeptide of claim 1 , wherein the GPCR is a protease activated receptor (PAR).

52. The polypeptide of claim 1 , wherein the GPCR is a thrombin receptor.

53. The polypeptide of claim 1 , wherein the GPCR is a P2Y 12 receptor.

54. A pharmaceutical composition comprising a polypeptide comprising:

a) a first domain comprising a third intracellular loop (i3 loop) or a fragment thereof of a G protein coupled receptor (GPCR), and

b) a second domain, attached to said first domain, wherein said second domain is a naturally or non-naturally occurring cell-penetrating, membrane-tethering moiety,

wherein said polypeptide is a GPCR agonist or antagonist and does not comprise an extracellular portion of the GPCR and said first domain is at least 3 contiguous amino acid residues; and a pharmaceutically acceptable carrier.

55. A polypeptide comprising:

a) a first domain comprising a third intracellular loop or a fragment thereof of a G protein coupled receptor, and

b) a second domain, attached to the first domain, wherein said second domain is a palmitoyl group,

wherein said polypeptide is a GPCR agonist or antagonist and does not comprise an extracellular portion of the GPCR and said first domain is at least 3 contiguous amino acid residues.