Identification of acidic residues in the extracellular loops of the seven-transmembrane domain of the human Ca2+ receptor critical for response to Ca2+ and a positive allosteric modulator

被引:69
作者
Hu, JX
Reyes-Cruz, G
Chen, WZ
Jacobson, KA
Spiegel, AM
机构
[1] NIDCD, Mol Pathophysiol Sect, NIH, Bethesda, MD 20892 USA
[2] NIDDK, Bioorgan Chem Lab, NIH, Bethesda, MD 20892 USA
关键词
D O I
10.1074/jbc.M207100200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
We investigated the role of the eight acidic residues in the extracellular loops (exo-loops) of the seven-transmembrane domain of the human Ca2+ receptor (hCaR) in receptor activation by Ca2+ and in response to a positive allosteric modulator, NPS R-568. Both in the context of the full-length receptor and of a truncated receptor lacking the extracellular domain (Rho-C-hCaR), we mutated each acidic residue to. alanine, singly and in combination, and tested the effect on expression of the receptor, on activation by Ca2+, and on NPS R-568 augmentation of sensitivity to Ca2+. Of the eight acidic residues, mutation of any of three in exo-loop 2, Asp(758), Glu(759), and Glu(767), increased the sensitivity of both the full-length hCaR and of Rho-C-hCaR to activation by Ca2+. Mutation of all five acidic residues in exo-loop 2, whether in the full-length receptor or in Rho-C-hCaR, impaired cell surface expression of the mutant receptor and thereby largely abolished response to Ca2+. Mutation of Glu(837) in exo-loop 3 to alanine did not alter Ca2+ sensitivity of the full-length receptor, but in both the latter context and in Rho-C-hCaR, alanine substitution of Glu(837) drastically reduced sensitivity to NPS R-568. Our data point to a key role of three specific acidic residues in exo-loop 2 in Wall activation and to Glu(837) at the junction between exo-loop 3 and transmembrane helix seven in response to NPS R-568. We speculate on the basis of these results that the three acidic residues we identified in exo-loop 2 help maintain an inactive conformation of the seven-transmembrane domain of the hCaR.
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收藏
页码:46622 / 46631
页数:10
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