The 69-84 amino acid region of the parathyroid hormone molecule is essential for the interaction of the hormone with the binding sites with carboxyl-terminal specificity.
We evaluated the competitive inhibitory effect of intact PTH, the amino-terminal PTH(1-34) fragment, and a series of truncated carboxyl-terminal PTH fragments on the binding of internally 35S-labeled human PTH(1-84) ([35S]hPTH(1-84)) to osteoblastic cells (ROS 17/2.8), in order to identify the minimum and critical elements within the PTH molecule for the interaction with the binding sites specific for the carboxyl-terminal region of the hormone. When the amino-terminal region of the PTH molecule was truncated stepwise, hPTH(35-84), hPTH(53-84) and hPTH(69-84), but not hPTH(70-84), significantly inhibited the [35S]hPTH(1-84) binding. On the other hand, the simple deletion of the carboxyl-terminal glutamine at position 84 of hPTH(53-84) [hPTH(53-83)] resulted in blunting the inhibitory effect of the peptide on the [35S]hPTH(1-84) binding. Furthermore, hPTH(35-84), hPTH(53-84) and hPTH(69-84), but not hPTH(70-84) nor hPTH(53-83), augmented the inhibitory effect of the amino-terminal PTH fragment [hPTH(1-34)] on the [35S]hPTH(1-84) binding. Of special interest was that the combination of hPTH(1-34) and hPTH(35-84) reproduced the inhibitory effect of unlabeled hPTH(1-84) on the [35S]hPTH(1-84) binding, on an equimolar basis. The 69-84 region of the PTH molecule thus appears to be crucial for binding to the carboxyl-terminal specific binding sites for PTH in osteoblasts. The interaction of the amino-terminal and carboxyl-terminal regions of a PTH molecule with their own respective binding sites seemed to occur in a fairly independent manner.
Takasu
H
H
Chugai Pharmaceutical Co., Ltd., Shizuoka, Japan.
Baba
H
H
Inomata
N
N
Uchiyama
Y
Y
Kubota
N
N
Kumaki
K
K
Matsumoto
A
A
Nakajima
K
K
Kimura
T
T
Sakakibara
S
S
Fujita
T
T
Chihara
K
K
Nagai
I
I
D000469:Alkaline Phosphatase / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D006801:Humans; D015592:Immunoradiometric Assay; D010281:Parathyroid Hormone / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D010446:Peptide Fragments / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins; D014407:Tumor Cells, Cultured
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D011994:Recombinant Proteins; D000469:Alkaline Phosphatase