Cloning and Properties of a Novel Natriuretic Peptide Receptor, NPR‐D

A novel natriuretic peptide receptor, which we have termed natriuretic peptide receptor D (NPR‐D), has been cloned and characterized. cDNAs related to the natriuretic peptide receptor (NPR) were amplified by PCR from a template of poly(A)‐rich RNA isolated from the eel gill. Sequencing of the PCR products revealed the presence of a new clone that showed about 70% sequence identity to the eel type‐C receptor, NPR‐C. The PCR fragment was used to determine the tissue distribution of the new NPR‐D message by an RNase protection assay, which gave the strongest signal in brain samples, and then used to screen a brain library to obtain a full‐length cDNA clone. The cDNA clone predicted a protein of 500 amino acids containing a signal sequence and a hydrophobic transmembrane segment. The predicted sequence also contained the NPR motif which is essential for the binding of natriuretic peptides. The protein NPR‐D was expressed in COS cells and shown to have high affinities for eel and rat natriuretic peptides. The newly cloned NPR‐D has a short cytoplasmic tail; in this respect, NPR‐C and NPR‐D are very similar and form a subfamily of the NPR family. Affinity labeling indicated that NPR‐D exists as a disulfide‐linked tetramer. This is a marked contrast to the homodimeric structure of NPR‐C. HS‐142‐1, a non‐peptide natriuretic peptide receptor antagonist of microbial origin previously shown to be selective for the guanylate‐cyclase‐coupled receptors NPR‐A and NPR‐B, competitively inhibited the binding of ¹²⁵I‐labeled eel natriuretic peptide to eel NPR‐D, whereas it did not affect the binding activity of eel NPR‐C, suggesting that HS‐142‐1 is an antagonist that recognizes the tetrameric structures of NPR since the guanylate‐cyclase‐coupled receptors have also been demonstrated to exist as tetramers.