Production of polyclonal antibody to the bovine adrenal atrial natriuretic factor-R1 receptor

Comparative binding study of rat natriuretic peptide receptor-A

The natriuretic peptide receptor-A (NPR-A) is involved in blood pressure and body fluid regulation in order to help maintain cardiovascular homeostasis. It has been shown that these biological effects are mediated through the natriuretic peptide family of hormones, which bind NPR-A according to the rank order ANP>BNP>>CNP. Previous studies performed with rat kidney papillary tissue suggested the existence of an heterologous NPR-A population since two binding components were obtained for pBNP32, one of high affinity (pK 9.4 +/- 0.1) and the other of lower affinity (pK 7.5 +/- 0.1), while in the same preparation rANP28 binding displayed the expected affinity (pK 10.22 +/- 0.01) and was best fitted with a model involving a single class of binding sites. This apparent heterogeneity of NPR-A in rat kidney papillae could be explained by the presence of two receptor isoforms or of monomeric and oligomeric forms of the same receptor. To investigate the NPR-A binding heterogeneity, we have cloned the rat NPR-A from PC12 cells and compared its pharmacological profile with that of the papillae. Our results with rat NPR-A transfected Cos-P cells show an equivalent pharmacological profile as with the rat tissue, i.e. a high affinity for rANP28 (pK 10.4 +/- 0.1) and two distinctive affinities for pBNP32 (pK 9.74 +/- 0.05 and 7.8 +/- 0.1). Although multiple receptor glycoforms were sometimes detectable by western blotting, only one molecular form was obtained by cross-linking with 125I-rANP28. It thus appears that NPR-A alone can account for the two binding components found in the rat papillae and that a single molecular form of the protein is implicated. We therefore propose that the oligomerization state of the receptors could be responsible for the apparent binding heterogeneity of rat NPR-A.

Glycosylation of asparagine 24 of the natriuretic peptide receptor-B is crucial for the formation of a competent ligand binding domain

UV cross-linking studies of the natriuretic peptide receptor-B (NPR-B) using radiolabeled C-type natriuretic peptide (CNP) indicate that only fully glycosylated receptors are capable of binding ligand. We therefore used site-directed mutagenesis to determine which potential glycosylation sites are occupied by carbohydrate, and the relevant mutants were characterized in order to understand the function of carbohydrate addition at those sites. Our results suggest that five of seven potential N-linked glycosylation sites are modified. In addition, mutation of asparagine 24 results in a loss of approximately 90% of receptor activity. This mutant is expressed at levels comparable to the wild-type receptor, and its activity is not significantly different from that of wild-type NPR-B in terms of EC50 for CNP. Ligand binding studies on this mutant further show that although there is no change in affinity for ligand, approximately 90% of receptor binding is lost. These data suggest that many of the mutant receptors are simply not properly folded. Our results indicate that glycosylation of asparagine 24 of NPR-B receptors may be critical for the formation of a competent ligand binding domain.

Glycosylation is critical for natriuretic peptide receptor-B function

Co-transfection of a truncated natriuretic peptide receptor-B (NPR-B) with the full length receptor results in a decrease of 60-80% in wild-type receptor activity. This reduction correlates with a loss of glycosylation of the full length NPR-B. This effect is dose-dependent, and occurs with no change in the glycosylation of the truncated receptor. Co-transfection of the full length NPR-B with other receptors yields similar results. These data suggest that glycosylation may be crucial for NPR-B function. Cross-linking studies further demonstrate that only fully glycosylated NPR-B receptors are able to bind ligand. Our data therefore argue that carbohydrate modification may be critical for NPR-B receptor ligand binding.