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Structure and function of the human calcium-sensing receptor: insights from natural and engineered mutations and allosteric modulators.

Hu J, Spiegel AM - J. Cell. Mol. Med. (2007 Sep-Oct)

Bottom Line: The human extracellular Ca(2+)-sensing receptor (CaR), a member of the G protein-coupled receptor family 3, plays a key role in the regulation of extracellular calcium homeostasis.It is one of just a few G protein-coupled receptors with a large number of naturally occurring mutations identified in patients.In contrast to the small sizes of its agonists, this large dimeric receptor consists of domains with topologically distinctive orthosteric and allosteric sites.

View Article: PubMed Central - PubMed

Affiliation: Molecular Signalling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA. jianxinh@niddk.nih.gov

ABSTRACT
The human extracellular Ca(2+)-sensing receptor (CaR), a member of the G protein-coupled receptor family 3, plays a key role in the regulation of extracellular calcium homeostasis. It is one of just a few G protein-coupled receptors with a large number of naturally occurring mutations identified in patients. In contrast to the small sizes of its agonists, this large dimeric receptor consists of domains with topologically distinctive orthosteric and allosteric sites. Information derived from studies of naturally occurring mutations, engineered mutations, allosteric modulators and crystal structures of the agonist-binding domain of homologous type 1 metabotropic glutamate receptor and G protein-coupled rhodopsin offers new insights into the structure and function of the CaR.

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Left, a model of the three-dimensional structure of the CaR VFT dimer: α helices in red, β sheets in yellow, loops and turns in green. Cysteines are shown. Both protomers and lobe 1, lobe 2, loop 2, and the putative orthosteric site of protomer 1 are labelled. Loop 2 is depicted arbitrarily in the model, since this loop was unstructured in all mGluR1 VFT crystal structures. The dimer interface runs along the vertical axis between the two protomers. Right, the CaR residues equivalent to those constituting the orthosteric site of the mGluR1. The residues in lobe 1 are shown in blue and the residues in lobe 2 are shown in red. An aster indicates the residue involved in naturally occurring inactivating CaR mutations (refer to Fig. 1), and artificial alanine mutations at the residues underlined impaired response of the receptor to extracellular Ca2+.
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fig02: Left, a model of the three-dimensional structure of the CaR VFT dimer: α helices in red, β sheets in yellow, loops and turns in green. Cysteines are shown. Both protomers and lobe 1, lobe 2, loop 2, and the putative orthosteric site of protomer 1 are labelled. Loop 2 is depicted arbitrarily in the model, since this loop was unstructured in all mGluR1 VFT crystal structures. The dimer interface runs along the vertical axis between the two protomers. Right, the CaR residues equivalent to those constituting the orthosteric site of the mGluR1. The residues in lobe 1 are shown in blue and the residues in lobe 2 are shown in red. An aster indicates the residue involved in naturally occurring inactivating CaR mutations (refer to Fig. 1), and artificial alanine mutations at the residues underlined impaired response of the receptor to extracellular Ca2+.

Mentions: The human CaSR gene is located on chromosome 3q13.3–21 and spans over 50 kb of genomic DNA. It has a coding region of 3234 bp, which is contained within six exons [11]. The CaR (hCaR) is expressed as a 1078 amino-acid polypeptide [12] and the mature protein starts from tyrosine 20 after cleavage of a hydrophobic signal peptide [13] (Fig. 1). It contains 11 potential N-linked glycosylation sites in its extracellular N-terminal (Fig. 2) [14]. Immunoblotting of the CaR expressed in transfected HEK-293 cells identifies two major bands under reducing conditions, corresponding to an incompletely processed, high mannose intracellular form the receptor at ∼130 kD and a fully glycosylated, cell surface-expressed form at ∼150 kD. Glycosylation does not appear to be crucial for CaR function, but rather for proper protein folding and trafficking [14, 15]. Immunoblotting of the CaR under reducing and non-reducing conditions revealed that the CaR is expressed as an intermolecular disulphide linked homodimer.


Structure and function of the human calcium-sensing receptor: insights from natural and engineered mutations and allosteric modulators.

Hu J, Spiegel AM - J. Cell. Mol. Med. (2007 Sep-Oct)

Left, a model of the three-dimensional structure of the CaR VFT dimer: α helices in red, β sheets in yellow, loops and turns in green. Cysteines are shown. Both protomers and lobe 1, lobe 2, loop 2, and the putative orthosteric site of protomer 1 are labelled. Loop 2 is depicted arbitrarily in the model, since this loop was unstructured in all mGluR1 VFT crystal structures. The dimer interface runs along the vertical axis between the two protomers. Right, the CaR residues equivalent to those constituting the orthosteric site of the mGluR1. The residues in lobe 1 are shown in blue and the residues in lobe 2 are shown in red. An aster indicates the residue involved in naturally occurring inactivating CaR mutations (refer to Fig. 1), and artificial alanine mutations at the residues underlined impaired response of the receptor to extracellular Ca2+.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4401263&req=5

fig02: Left, a model of the three-dimensional structure of the CaR VFT dimer: α helices in red, β sheets in yellow, loops and turns in green. Cysteines are shown. Both protomers and lobe 1, lobe 2, loop 2, and the putative orthosteric site of protomer 1 are labelled. Loop 2 is depicted arbitrarily in the model, since this loop was unstructured in all mGluR1 VFT crystal structures. The dimer interface runs along the vertical axis between the two protomers. Right, the CaR residues equivalent to those constituting the orthosteric site of the mGluR1. The residues in lobe 1 are shown in blue and the residues in lobe 2 are shown in red. An aster indicates the residue involved in naturally occurring inactivating CaR mutations (refer to Fig. 1), and artificial alanine mutations at the residues underlined impaired response of the receptor to extracellular Ca2+.
Mentions: The human CaSR gene is located on chromosome 3q13.3–21 and spans over 50 kb of genomic DNA. It has a coding region of 3234 bp, which is contained within six exons [11]. The CaR (hCaR) is expressed as a 1078 amino-acid polypeptide [12] and the mature protein starts from tyrosine 20 after cleavage of a hydrophobic signal peptide [13] (Fig. 1). It contains 11 potential N-linked glycosylation sites in its extracellular N-terminal (Fig. 2) [14]. Immunoblotting of the CaR expressed in transfected HEK-293 cells identifies two major bands under reducing conditions, corresponding to an incompletely processed, high mannose intracellular form the receptor at ∼130 kD and a fully glycosylated, cell surface-expressed form at ∼150 kD. Glycosylation does not appear to be crucial for CaR function, but rather for proper protein folding and trafficking [14, 15]. Immunoblotting of the CaR under reducing and non-reducing conditions revealed that the CaR is expressed as an intermolecular disulphide linked homodimer.

Bottom Line: The human extracellular Ca(2+)-sensing receptor (CaR), a member of the G protein-coupled receptor family 3, plays a key role in the regulation of extracellular calcium homeostasis.It is one of just a few G protein-coupled receptors with a large number of naturally occurring mutations identified in patients.In contrast to the small sizes of its agonists, this large dimeric receptor consists of domains with topologically distinctive orthosteric and allosteric sites.

View Article: PubMed Central - PubMed

Affiliation: Molecular Signalling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA. jianxinh@niddk.nih.gov

ABSTRACT
The human extracellular Ca(2+)-sensing receptor (CaR), a member of the G protein-coupled receptor family 3, plays a key role in the regulation of extracellular calcium homeostasis. It is one of just a few G protein-coupled receptors with a large number of naturally occurring mutations identified in patients. In contrast to the small sizes of its agonists, this large dimeric receptor consists of domains with topologically distinctive orthosteric and allosteric sites. Information derived from studies of naturally occurring mutations, engineered mutations, allosteric modulators and crystal structures of the agonist-binding domain of homologous type 1 metabotropic glutamate receptor and G protein-coupled rhodopsin offers new insights into the structure and function of the CaR.

Show MeSH
Related in: MedlinePlus