Possible identification of novel natriuretic peptide receptor phosphorylation sites by alanine/glutamate mutagenesis

Background Natriuretic peptide receptors A (NPR-A) and B (NPR-B) are transmembrane guanylyl cyclases that regulate blood pressure, heart size and long bone growth. Unlike most cell surface receptors that are desensitized by direct phosphorylation, phosphorylation of natriuretic peptide receptors is essential for activation, and dephosphorylation causes their desensitization. While there are six and five known phosphorylation sites within NPR-A and NPRB, respectively, studies in homologous sea urchin guanylyl cyclase receptors indicate the presence of 15–17 moles of phosphate per mole of receptor, suggesting additional natriuretic peptide receptor phosphorylation sites remain to be identified. The purpose of this study was to identify novel natriuretic peptide receptor phosphorylation sites by evaluating functional consequences of individual glutamate or alanine substitutions of candidate residues in order to mimic the effects of a phosphorylated or dephosphorylated residue, respectively.