Enhanced Activity in Parathyroid Hormone-(1-14) and -(1-11): Novel Peptides for Probing Ligand-Receptor Interactions

Abstract

The amino-terminal portion of PTH is critical for PTH-1 receptor (P1Rc) activation. In exploring this component of the ligand receptor interaction, we recently showed that the agonist potency of the weakly active PTH-(1–14)NH2 peptide can be enhanced by natural amino acid substitutions at several positions, including position 11 (normally leucine). Here we show that the potency of PTH-(1–14)NH2 can be enhanced by using nonnatural amino acids that increase the length and polarizability of the position 11 side-chain. Thus, in LLC-PK1 cells stably expressing high levels of the human P1Rc,[ homoarginine([Har)11]PTH-(1–14)NH2 was 30-fold more potent for cAMP production than was native PTH-(1–14)NH2. Combining the homoarginine-11 substitution with other recently identified activity-enhancing substitutions yielded[ Ala3,12,Gln10,Har11,Trp14]PTH-(1–14)NH2, which was 1500-fold more potent than PTH-(1–14)NH2 (EC50 = 0.12 ± 0.04 and 190 ± 20μ m, respectively) and only 63-fold less potent than PTH-(1–34) (EC50 = 1.9 ± 0.5 nm). The even shorter analog[ Ala3,Gln10,Har11]PTH-(1–11)NH2 was also a full cAMP agonist (EC50 = 3.1 ± 1.5μ m). Receptor mutations at Phe184 and Leu187 located near the boundary of the amino-terminal domain and transmembrane domain-1 severely impaired responsiveness to the PTH-(1–11) analog. Overall, these studies demonstrate that PTH analogs of only 11 amino acids are sufficient for activation of the PTH-1 receptor through interaction with its juxtamembrane region.