Jüppner H, Schipani E, Bringhurst F R, McClure I, Keutmann H T, Potts J T, Kronenberg H M, Abou-Samra A B, Segre G V, Gardella T J
Department of Pediatrics, Massachusetts General Hospital, Boston.
Endocrinology. 1994 Feb;134(2):879-84. doi: 10.1210/endo.134.2.8299582.
The recombinant human PTH/PTH-related peptide (PTHrP) receptor, when transiently expressed in COS-7 cells, binds [Nle8,18,Tyr34] bovine PTH-(7-34)amide [PTH-(7-34)], human PTH-(10-34)amide [PTH-(10-34)], and bovine PTH-(15-34)amide [PTH-(15-34)] with at least 50-fold higher affinity than does the rat receptor homolog. In contrast, PTH-(1-34) binding affinities are similar for both receptor homologs. To map those areas of the PTH/PTHrP receptors that determine the binding specificity for carboxyl-terminal fragments of PTH-(1-34), we constructed chimeric rat/human PTH/PTHrP receptors. These bound PTH-(1-34) with normal affinity and, therefore, must have an overall conformation that resembles that of native receptors. Chimeras with the amino-terminal extracellular domain of the human PTH/PTHrP receptor have a considerably higher binding affinity for PTH-(7-34), PTH-(10-34), and PTH-(15-34) than do the reciprocal receptor constructs in which the amino-terminal region is from the rat PTH/PTHrP receptor. The opossum PTH/PTHrP receptor homolog also binds PTH-(7-34) with higher affinity than the rat receptor, and studies of rat/opossum chimeras confirm the importance of the amino-terminal extracellular domain in determining the PTH-(7-34) binding specificity. Mutant rat and human PTH/PTHrP receptors in which either residues 61-105 of the extracellular region or most of the intracellular tail were deleted have PTH-(7-34) binding characteristics indistinguishable from those of either wild-type receptor. These findings indicate that the amino-terminal extracellular region of the PTH/PTHrP receptor contains a domain(s) that largely determines the binding affinity of amino-terminally truncated PTH analogs. This region, therefore, is likely to constitute a site for ligand-receptor interaction.
重组人甲状旁腺激素/甲状旁腺激素相关肽（PTHrP）受体在COS-7细胞中瞬时表达时，与[异亮氨酸8,18,酪氨酸34]牛PTH-（7-34）酰胺[PTH-（7-34）]、人PTH-（10-34）酰胺[PTH-（10-34）]和牛PTH-（15-34）酰胺[PTH-（15-34）]的结合亲和力比大鼠受体同源物至少高50倍。相比之下，两种受体同源物对PTH-（1-34）的结合亲和力相似。为了确定PTH/PTHrP受体中决定对PTH-（1-34）羧基末端片段结合特异性的区域，我们构建了嵌合大鼠/人PTH/PTHrP受体。这些受体以正常亲和力结合PTH-（1-34），因此其整体构象必定类似于天然受体。与人PTH/PTHrP受体氨基末端细胞外结构域相同的嵌合体对PTH-（7-34）、PTH-（10-34）和PTH-（15-34）的结合亲和力，比氨基末端区域来自大鼠PTH/PTHrP受体的反向受体构建体高得多。负鼠PTH/PTHrP受体同源物对PTH-（7-34）的结合亲和力也高于大鼠受体，对大鼠/负鼠嵌合体的研究证实了氨基末端细胞外结构域在决定PTH-（7-34）结合特异性方面的重要性。细胞外区域61-105位残基或大部分细胞内尾部被缺失的突变大鼠和人PTH/PTHrP受体，其PTH-（7-34）结合特性与野生型受体无明显差异。这些发现表明，PTH/PTHrP受体的氨基末端细胞外区域包含一个很大程度上决定氨基末端截短的PTH类似物结合亲和力的结构域。因此，该区域可能构成配体-受体相互作用的位点。
