title: Forced homodimerization by site-directed mutagenesis alters guanylyl cyclase activity of natriuretic peptide receptor B.
abstract: Natriuretic peptides mediate their physiologic effects through activation of membrane-bound, guanylyl cyclase-coupled receptors (NPRs). Receptor dimerization is an important feature of signal transduction. This study was aimed at characterizing structurally important residues of the extracellular ligand-binding domain of NPR-B for receptor dimerization and cGMP generation. Deletion mutagenesis was used to replace cysteine residues at positions 53 (C53S), 417 (C417S), and 426 (C426S) by serine. Receptor expression, dimerization, whole-cell cGMP response, and guanylyl cyclase activity of membrane fractions were determined in stably transfected COS-7 cells. C53S, C417S, and C426S mutants were expressed and found to form disulfide-bridged covalent dimers. In contrast to NPR-B and C53S, C417S and C426S mutants displayed constitutive activity in whole cells (C417S, 146+/-12%, P<0.01; C426S, 153+/-7% of ligand-independent NPR-B cGMP generation, P<0.01). The cGMP response of C417S and C426S mutants in whole cells was dose dependent and approximately 4 times lower than that in NPR-B, whereas it was blunted in C53S-transfected cells (1 micromol/L CNP, NPR-B 2868+/-436%; C53S, 206+/-16% of control, P<0.001 vs NPR-B, C417S, and C426S). Guanylyl cyclase assay in transfected cells confirmed the constitutive activity of C417S and C426S mutants. These data suggest that receptor dimerization by covalent disulfide bridges alters ligand-independent as well as ligand-dependent receptor activity. Localization of the crosslink in relation to the cell membrane is important for configuration of the extracellular domain and the consecutive signal transduction.
authors.affiliation: Max-Delbrueck-Center for Molecular Medicine, Berlin-Buch, Berlin, Germany. langenit@nhlbi.nih.gov
authors.forename: Thomas
authors.initials: T
authors.lastname: Langenickel
authors.forename: Jens
authors.initials: J
authors.lastname: Buttgereit
authors.forename: Ines
authors.initials: I
authors.lastname: Pagel
authors.forename: Rainer
authors.initials: R
authors.lastname: Dietz
authors.forename: Roland
authors.initials: R
authors.lastname: Willenbrock
authors.forename: Michael
authors.initials: M
authors.lastname: Bader
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D019281:Dimerization; D006162:Guanylate Cyclase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017461:Receptors, Atrial Natriuretic Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000099242:Atrial Natriuretic Factor Receptor B
chemical_list: D006162:Guanylate Cyclase; D012333:RNA, Messenger; D017461:Receptors, Atrial Natriuretic Factor; D000099242:Atrial Natriuretic Factor Receptor B