Modified ghrelin peptides

1. A DNA coding for an amino acid sequence of a peptide-type compound,

wherein the amino acid sequence comprises one amino acid sequence selected from the group consisting of amino acid sequences set forth in SEQ ID NOs:2, 10, 16, 17, 22, 25, 26, 27, 28, 29, 30 and 31, wherein one amino acid is deleted, replaced and/or added, and wherein said one amino acid is not deleted, replaced and/or added at the first to fourth amino acid from the amino-terminal in said amino acid sequence,

provided that a natural product is excluded, and

wherein the amino acid sequence as modified above is a sequence of a precursor for producing the peptide-type compounds which binds to a growth hormone secretagogue receptor, increases the intracellular calcium ion concentration, or induces growth hormone secretion.

2. An expression vector comprising a desired gene wherein the vector is to express the desired gene, and a promoter is linked operatively upstream of said gene, and the desired gene is DNA of claim 1 .

3. An expression vector comprising a desired gene wherein the vector is to express the desired gene, and a promoter is linked operatively upstream of said gene, wherein the desired gene and/or the promoter is heterologous or heterogeneous to the vector, wherein the desired gene is a DNA coding for an amino acid sequence of a peptide-type compound,

wherein the amino acid sequence consists of one amino acid sequence selected from the group consisting of (A) the amino acid sequence set forth in SEQ ID NOs:1, 2, 3, 8, 9, 10, 11, 16, 17, 22, 25, 26, 27, 28, 29, 30 and 31, (B) a variant of the amino acid sequence set forth in SEQ ID NOs:1, 2, 3, 10, 11, 16, 17, 22, 25, 26, 27, 28, 29, 30 and 31, wherein one amino acid is deleted, replaced and/or added, (C) a variant of the amino acid sequence set forth in SEQ ID NO:8 wherein one amino acid is added, and (D) a variant of the amino acid sequence set forth in SEQ ID NO:9 wherein one amino acid is deleted and/or replaced,

wherein said one amino acid is not deleted, replaced and/or added at the first to fourth amino acid from the amino-terminal in said amino acid sequence, and

wherein the amino acid sequence is a sequence of a precursor for producing the peptide-type compounds which binds to a growth hormone secretagogue receptor, increases the intracellular calcium ion concentration, or induces growth hormone secretion.

4. An expression vector comprising a desired gene wherein the vector is to express the desired gene, and a promoter is linked operatively upstream of said gene wherein the desired gene and/or the promoter is heterologous or heterogeneous to the vector, and wherein the desired gene is a DNA consisting of one nucleotide sequence selected from the group consisting of positions 100-183 of SEQ ID NO:6, positions 103-186 of SEQ ID NO:7, positions 100-180 of SEQ ID NO:14, positions 103-183 of SEQ ID NO:15, positions 81-164 of SEQ ID NO:20, positions 81-161 of SEQ ID NO:21, positions 16-96 of SEQ ID NO:24, positions 135-197 of SEQ ID NO:36, positions 119-199 of SEQ ID NO:37, positions 63-131 of SEQ ID NO:38, positions 63-122 of SEQ IDNO:39, positions 103-114 of SEQ ID NO:7, positions 103-123 of SEQ ID NO:7 and positions 103-132 of SEQ ID NO:7, and

wherein the DNA codes for an amino acid sequence that is a sequence of a precursor for producing a peptide-type compound which binds to a growth hormone secretagogue receptor, increases the intracellular calcium ion concentration, or induces growth hormone secretion.

5. A transformed cell comprising the expression vector of claim 2 .

6. A transformed cell comprising the expression vector of claim 3 .

7. A transformed cell comprising the expression vector of claim 4 .

8. A method for producing a peptide-type compound which comprises culturing the transformed cell of claim 6 in a liquid medium including one or more selected from the group consisting of a carbon source, a nitrogen source, vitamins, growth promoters and serum, and recovering the peptide-type compound from the culture,

wherein the transformed cell is capable of cutting a suitable site in a precursor polypeptide of said peptide and acylating the serine residue at the third position in said peptide, and

wherein the recovery step includes separating the peptide-type compound from the culture and purifying the peptide-type compound.

9. The method of claim 8 , wherein the transformed cell is capable of binding a fatty acid via an ester linkage to a side-chain hydroxyl group of an amino acid or via a thioester linkage to a side-chain mercapto group of an amino acid in the peptide-type compound, and wherein the recovered peptide-type compound comprises an amino acid with a fatty acid bound via an ester linkage to a side-chain hydroxyl group of the amino acid or an amino acid with a fatty acid bound via a thioester linkage to a side-chain mercapto group of the amino acid.

10. The method of claim 8 , wherein the transformed cell is capable of an acylation activity of binding a fatty acid via an ester linkage to a side-chain hydroxyl group of serine, and wherein the recovered peptide-type compound comprises a serine with a fatty acid bound via an ester linkage to a side-chain hydroxyl group of the serine.

11. The method of claim 8 , wherein the transformed cell is capable of an acylation activity of binding a fatty acid via an ester linkage to a side-chain hydroxyl group of threonine, and wherein the recovered peptide-type compound comprises a threonine with a fatty acid bound via an ester linkage to a side-chain hydroxyl group of the threonine.

12. The method of claim 8 , further comprising acylating with an acyl group containing 2 to 35 carbon atoms an amino acid of the recovered peptide-type compound.

13. The method of claim 8 , further comprising acylating with octanoyl an amino acid of the recovered peptide-type compound.

14. The method of claim 8 , wherein the second or third amino acid residue from the amino-terminal of the amino acid sequence of the peptide-type compound is a modified amino acid in which:

(1) one saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the alpha carbon atom of the amino acid by an ester, ether, thioether, thioester, amide, carbamide, thiocarbamide or disulfide linkage;

(2) one saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the alpha carbon atom of the amino acid by an alkylene group containing 1 to 10 carbon atoms and by an ester, ether, thioether, thioester, amide, carbamide, thiocarbamide or disulfide linkage; or

(3) one saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the alpha carbon atom of the amino acid, and

wherein said peptide-type compound or pharmaceutically acceptable salt thereof increases intracellular calcium ion concentration, is produced.

15. The method of claim 14 , wherein the second or third amino acid residue from the N-terminal of the amino acid sequence is serine and the serine residue is modified at the side-chain hydroxyl group wherein the peptide-type compound increases intracellular calcium ion concentration.

16. The method of claim 14 , wherein the modified amino acid is serine in which the side-chain hydroxy group is converted into a group represented by —OCO—Z1 wherein Z1 is hydrogen or a saturated or unsaturated alkyl chain containing 1 to 50 carbon atoms.

17. The method of claim 14 , wherein the modified amino acid residue is one in which a fatty acid is bound to the side-chain hydroxy group via an ester bond.

18. The method of claim 17 , wherein the fatty acid contains 2 to 35 carbon atoms.

19. The method of claim 18 , wherein the fatty acid is selected from fatty acids containing 2, 4, 6, 8, 10, 12, 14, 16 or 18 carbon atoms.

20. The method of claim 19 , wherein the fatty acid is selected from octanoic acid, a monoene fatty acid thereof and a polyene fatty acid thereof.

21. The method of claim 19 , wherein the fatty acid is selected from decanoic acid, a monoene fatty acid thereof and a polyene fatty acid thereof.

22. The method of claim 14 , in which the side chain hydroxy group of serine at the third position from the amino-terminal in said amino acid sequence is acylated with an acyl group containing 2 to 35 carbon atoms.

23. The method of claim 14 , in which the serine at the third position from the amino-terminal in said amino acid sequence is converted into threonine, and in which the side-chain hydroxy group of threonine at the third position from the amino-terminal is acylated with an acyl group containing 2 to 35 carbon atoms.

24. The method of claim 14 , in which the side-chain hydroxy group of serine at the third position from the amino-terminal is acylated with octanoyl.

25. The method of claim 14 , wherein the compound has additionally an activity of inducing secretion of growth hormone.

26. The method of claim 14 , which comprises a basic amino acid bound to the carboxyl-terminal.

27. The method of claim 14 , wherein the amino-terminal is modified with a saturated or unsaturated alkyl group or an acyl group containing one or more carbon atoms, and/or the hydroxy group in the carboxyl group at the carboxyl-terminal of said amino acid sequence is OZ or is replaced by NR 2 R 3 wherein Z is a pharmaceutically acceptable cation or a lower branched or linear alkyl group, and R 2 and R 3 are the same or different and represent hydrogen or a lower branched or linear alkyl group.

28. The method of claim 27 , wherein the carboxyl-terminal of said amino acid sequence is an amide derivative with a substituted basic amino acid.

29. The method of claim 14 , wherein the peptide-type compound or a pharmaceutically acceptable salt thereof which consists of an amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 11 is produced.

30. The method of claim 8 , wherein the second or third amino acid residue from the amino-terminal of the amino acid sequence of the peptide-type compound is a modified amino acid selected from

(i) serine, threonine, tyrosine or oxyproline, in which the side-chain hydroxy group is converted into a group represented by —OCO—Z 1 , —OCS—Z 1 or —O—Z 3 , or

(ii) cysteine in which the side-chain mercapto group is converted into —SCO—Z 1 , —SCS—Z 1 , —S—Z 3 or —S—S—Z 8 , or

(iii) lysine or arginine, in which the side-chain amino group is converted into —NH—CO—Z 2 , —NH—CS—Z 2 , —N(Z 5 )(Z 6 ), —NH—CO—NH—Z 7 or —NH—CS—NH—Z 7 , or

(iv) histidine or tryptophan, in which the side-chain amino group is converted into a group represented by the formula:

wherein Z 1 is hydrogen or a saturated or unsaturated alkyl chain containing 1 to 50 carbon atoms, Z 2 , Z 3 , Z 4 , Z 5 , Z 6 , Z 7 and Z 8 are the same or different and represent hydrogen or a saturated or unsaturated alkyl chain containing 1 to 10 carbon atoms,

wherein said peptide-type compound or pharmaceutically acceptable salt thereof increases intracellular calcium ion concentration,

is produced.

31. The method of claim 30 , wherein the second or third amino acid residue from the N-terminal of the amino acid sequence is serine and the serine residue is modified at the side-chain hydroxyl group wherein the peptide-type compound increases intracellular calcium ion concentration.

32. The method of claim 30 , wherein the modified amino acid is serine in which the side-chain hydroxy group is converted into a group represented by —OCO—Z1 wherein Z1 is hydrogen or a saturated or unsaturated alkyl chain containing 1 to 50 carbon atoms.

33. The method of claim 30 , wherein the modified amino acid residue is one in which a fatty acid is bound to the side-chain hydroxy group via an ester bond.

34. The method of claim 30 , wherein the fatty acid contains 2 to 35 carbon atoms.

35. The method of claim 34 , wherein the fatty acid is selected from fatty acids containing 2, 4, 6, 8, 10, 12, 14, 16 or 18 carbon atoms.

36. The method of claim 35 , wherein the fatty acid is selected from octanoic acid, a monoene fatty acid thereof and a polyene fatty acid thereof.

37. The method of claim 35 , wherein the fatty acid is selected from decanoic acid, a monoene fatty acid thereof and a polyene fatty acid thereof.

38. The method of claim 30 , in which the side chain hydroxy group of serine at the third position from the amino-terminal in said amino acid sequence is acylated with an acyl group containing 2 to 35 carbon atoms.

39. The method of claim 30 , in which the serine at the third position from the amino-terminal in said amino acid sequence is converted into threonine, and in which the side-chain hydroxy group of threonine at the third position from the amino-terminal is acylated with an acyl group containing 2 to 35 carbon atoms.

40. The method of claim 30 , in which the side-chain hydroxy group of serine at the third position from the amino-terminal is acylated with octanoyl.

41. The method of claim 30 , wherein the compound has additionally an activity of inducing secretion of growth hormone.

42. The method of claim 30 , which comprises a basic amino acid bound to the carboxyl-terminal.

43. The method of claim 30 , wherein the amino-terminal is modified with a saturated or unsaturated alkyl group or an acyl group containing one or more carbon atoms, and/or the hydroxy group in the carboxyl group at the carboxyl-terminal of said amino acid sequence is OZ or is replaced by NR 2 R 3 wherein Z is a pharmaceutically acceptable cation or a lower branched or linear alkyl group, and R 2 and R 3 are the same or different and represent hydrogen or a lower branched or linear alkyl group.

44. The method of claim 43 , wherein the carboxyl-terminal of said amino acid sequence is an amide derivative with a substituted basic amino acid.

45. The method of claim 30 , wherein the peptide-type compound or a pharmaceutically acceptable salt thereof which consists of an amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 11 is produced.

46. The method of claim 8 , wherein the peptide-type compound or a pharmaceutically acceptable salt thereof which comprises the amino acid sequence of SEQ ID NO: 3, in which the side-chain hydroxy group of the serine at the third position from the amino-terminal is acylated with n-octanoyl, and said peptide-type compound increases intracellular calcium ion concentration is produced.

47. A method for producing a peptide-type compound which comprises culturing the transformed cell of claim 6 in a liquid medium including one or more selected from the group consisting of a carbon source, a nitrogen source, vitamins, growth promoters and serum, and recovering the peptide-type compound from the culture,

wherein the recovery step includes separating the peptide-type compound from the culture and purifying the peptide-type compound, and

chemically modifying an amino acid of the recovered peptide-type compound by acylating the amino acid at the third position of the peptide.

48. A method for producing a peptide-type compound comprising (a) the amino acid sequence set forth in SEQ ID NO: 2 or (b) an amino acid sequence having any one of amino acid sequences selected from the group consisting of

(1) amino acid sequence of amino acids 1 to 4,

(2) amino acid sequence of amino acids 1 to 5,

(3) amino acid sequence of amino acids 1 to 6,

(4) amino acid sequence of amino acids 1 to 7,

(5) amino acid sequence of amino acids 1 to 8,

(6) amino acid sequence of amino acids 1 to 9, and

(7) amino acid sequence of amino acids 1 to 10

from the amino-terminal of the amino acid sequence set forth in SEQ ID NO: 2 wherein at least one amino acid is deleted, replaced and/or added in a part outside said amino acid sequences (1) to (7), or a pharmaceutically acceptable salt thereof by genetic recombination technology,

which comprises transforming the vector of claim 3 into a host cell, wherein the host cell is capable of acylating a side chain of one or more amino acid(s) in said peptide, then culturing the resulting transformed cell in a liquid medium including one or more selected from the group consisting of a carbon source, a nitrogen source, vitamins, growth promoters and serum, and recovering the desired peptide-type compound from the culture wherein the recovery step includes separating the peptide-type compound from the culture and purifying the peptide-type compound.

49. The method of claim 48 , wherein the recovered peptide-type compound is further modified in at least one amino acid in positions 1 to 5 from the amino acid terminal as an acylated amino acid in which:

(a) a saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the α carbon atom of the amino acid by an ester, ether, thioester, thioether, amide, carbamide, thiocarbamide or disulfide linkage;

(b) a saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the α carbon atom of the amino acid by an alkylene group containing 1 to 10 carbon atoms and by an ester, ether, thioester, thioether, amide, carbamide, thiocarbamide or disulfide, linkage; or

(c) a saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the α carbon atom of the amino acid.

50. The method of claim 49 , wherein the amino acid sequence comprises one amino acid sequence selected from the group consisting of amino acid sequences set forth in SEQ ID NOs: 1, 3, 8, 9, 10, 11, 16, 17, 22, 25, 26, 27, 28, 29, 30 and 31.

51. The method of claim 48 , wherein the amino acid sequence comprises one amino acid sequence selected from the group consisting of amino acid sequences set forth in SEQ ID NOs: 1, 3, 8, 9, 10, 11, 16, 17, 22, 25, 26, 27, 28, 29, 30 and 31.

52. A method for producing a peptide-type compound comprising (a) the amino acid sequence set forth in SEQ ID NO: 2 or (b) an amino acid sequence having any one of amino acid sequences selected from the group consisting of

(1) amino acid sequence of amino acids 1 to 4,

(2) amino acid sequence of amino acids 1 to 5,

(3) amino acid sequence of amino acids 1 to 6,

(4) amino acid sequence of amino acids 1 to 7,

(5) amino acid sequence of amino acids 1 to 8,

(6) amino acid sequence of amino acids 1 to 9, and

(7) amino acid sequence of amino acids 1 to 10

from the amino-terminal of the amino acid sequence set forth in SEQ ID NO: 2 wherein at least one amino acid is deleted, replaced and/or added in a part outside said amino acid sequences (1) to (7), or a pharmaceutically acceptable salt thereof by genetic recombination technology,

which comprises transforming the vector of claim 4 into a host cell, wherein the host cell is capable of acylating a side chain of one or more amino acid(s) in said peptide, then culturing the resulting transformed cell in a liquid medium including one or more selected from the group consisting of a carbon source, a nitrogen source, vitamins, growth promoters and serum, and recovering the desired peptide-type compound from the culture wherein the recovery step includes separating the peptide-type compound from the culture and purifying the peptide-type compound.

53. The method of claim 52 , wherein the recovered peptide-type compound is further modified in at least one amino acid in positions 1 to 5 from the amino acid terminal as an acylated amino acid in which:

(a) a saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the α carbon atom of the amino acid by an ester, ether, thioester, thioether, amide, carbamide, thiocarbamide or disulfide linkage;

(b) a saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the α carbon atom of the amino acid by an alkylene group containing 1 to 10 carbon atoms and by an ester, ether, thioester, thioether, amide, carbamide, thiocarbamide or disulfide, linkage; or

(c) a saturated or unsaturated alkyl chain containing 1 to 35 carbon atoms is introduced at the α carbon atom of the amino acid.

54. The method of claim 53 , wherein the amino acid sequence comprises one amino acid sequence selected from the group consisting of amino acid sequences set forth in SEQ ID NOs: 1, 3, 8, 9, 10, 11, 16, 17, 22, 26, 28, 29, and 30.

55. The method of claim 52 , wherein the amino acid sequence comprises one amino acid sequence selected from the group consisting of amino acid sequences set forth in SEQ ID NOs: 1, 3, 8, 9, 10, 11, 16, 17, 22, 26, 28, 29, and 30.

56. A method for producing a peptide-type compound which comprises culturing the transformed cell of claim 7 in a liquid medium including one or more selected from the group consisting of a carbon source, a nitrogen source, vitamins, growth promoters and serum, and recovering the peptide-type compound from the culture,

wherein the transformed cell is capable of cutting a suitable site in a precursor polypeptide of said peptide and acylating the serine residue at the third position in said peptide, and

wherein the recovery step includes separating the peptide-type compound from the culture and purifying the peptide-type compound.

57. A method for producing a peptide-type compound which comprises culturing the transformed cell of claim 7 in a liquid medium including one or more selected from the group consisting of a carbon source, a nitrogen source, vitamins, growth promoters and serum, and recovering the peptide-type compound from the culture,

wherein the recovery step includes separating the peptide-type compound from the culture and purifying the peptide-type compound, and chemically modifying an amino acid of the recovered peptide-type compound by acylating the amino acid at the third position of the peptide.