Modifications of position 12 in parathyroid hormone and parathyroid hormone related protein: toward the design of highly potent antagonists.
Truncated N-terminal fragments of parathyroid hormone (PTH), [Tyr34]bovine PTH(7-34)NH2, and parathyroid hormone related protein (PTHrP), PTHrP(7-34)NH2, inhibit [Nle8,18,[125I]iodo-Tyr34]-bPTH(1-34)NH2 binding and PTH-stimulated adenylate cyclase in bone and kidney assays. However, the receptor interactions of these peptides are 2-3 orders of magnitude weaker than those of their agonist counterparts. To produce an antagonist with increased receptor-binding affinity but lacking agonist-like properties, structure-function studies were undertaken. Glycine at position 12 (present in all homologues of PTH and in PTHrP), which is predicted in both hormones to participate in a beta-turn, was examined by substituting conformational reporters, such as D- or L-Ala, Pro, and alpha-aminoisobutyric acid (Aib), in both agonist and antagonist analogues. Except for N-substituted amino acids, which substantially diminished potency, substitutions were well tolerated, indicating that this site can accept a wide latitude of modifications. To augment receptor avidity, hydrophobic residues compatible with helical secondary structure were introduced. Incorporation of the nonnatural amino acids D-Trp, D-alpha-naphthylalanine (D-alpha-Nal), or D-beta-Nal into either [Tyr34]bPTH(7-34)NH2 or [Nle8,18,Tyr34]bPTH(7-34)NH2 resulted in antagonists that were about 10-fold more active than their respective 7-34 parent compound. Similarly, [D-Trp12]PTHrP(7-34)NH2 was 6 times more potent than the unsubstituted peptide but retained partial agonistic properties, although markedly reduced, similar to PTHrP(7-34)NH2. The antagonistic potentiating effect was configurationally specific.(ABSTRACT TRUNCATED AT 250 WORDS)
Chorev
M
M
Merck Sharp & Dohme Research Laboratories, West Point, Pennsylvania 19486.
Goldman
M E
ME
McKee
R L
RL
Roubini
E
E
Levy
J J
JJ
Gay
C T
CT
Reagan
J E
JE
Fisher
J E
JE
Caporale
L H
LH
Golub
E E
EE
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008969:Molecular Sequence Data; D010281:Parathyroid Hormone / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D044162:Parathyroid Hormone-Related Protein; D011487:Protein Conformation; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D012689:Sequence Homology, Nucleic Acid; D013329:Structure-Activity Relationship
C470121:PTHLH protein, human; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D000262:Adenylyl Cyclases