title: Allotopic antagonism of the non-peptide atrial natriuretic peptide (ANP) antagonist HS-142-1 on natriuretic peptide receptor NPR-A.
abstract: The microbial polysaccharide HS-142-1 has been documented as an antagonist of natriuretic peptides. It inhibits activation and peptide binding to both guanylate receptors natriuretic peptide receptor (NPR)-A and NPR-B, but has no effect on the non-cyclase receptor NPR-C. At first sight the effect of HS-142-1 on peptide binding appears to be surmountable, suggesting that it might be competitive despite its chemically divergent nature. We explored its mode of action on wild-type NPR-A (WT), on a disulphide-bridged constitutively active mutant (C423S) and on truncated mutants lacking either their cytoplasmic domain (DeltaKC) or both the cytoplasmic and the transmembrane domains (ECD). On the WT, HS-142-1 inhibited atrial natriuretic peptide (ANP) binding with a pK value of 6.51 +/- 0.07 (K(d)=0.31 microM). It displayed a similar effect on the C423S mutant (pK=6.31 +/- 0.11), indicating that its action might not be due to interference with receptor dimerization. HS-142-1 also inhibited ANP binding to DeltaKC with a pK of 7.05 +/- 0.05 (K(d)=0.089 microM), but it was inactive on ANP binding to ECD at a concentration of 10(-4) M, suggesting that the antagonism was not competitive at the peptide-binding site located on the ECD and that the transmembrane domain might be required. HS-142-1 also enhanced dissociation of NPR-A-bound (125)I-ANP in the presence of excess unlabelled ANP, implying an allotopic (allosteric) mode of action for the antagonist.
authors.affiliation: Département de Pharmacologie, Faculté de Médecine, Université de Montréal, C.P. 6128, Centre-Ville, Montreal, Quebec, H3C-3J7, Canada.
authors.forename: Hugo
authors.initials: H
authors.lastname: Poirier
authors.forename: Jean
authors.initials: J
authors.lastname: Labrecque
authors.forename: Julie
authors.initials: J
authors.lastname: Deschênes
authors.forename: André
authors.initials: A
authors.lastname: DeLéan
mesh_terms: D000494:Allosteric Regulation; D009320:Atrial Natriuretic Factor / Q000378:metabolism; D002460:Cell Line; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D011134:Polysaccharides / Q000494:pharmacology*; D011485:Protein Binding; D017461:Receptors, Atrial Natriuretic Factor / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C072551:HS 142-1; D007457:Iodine Radioisotopes; D011134:Polysaccharides; D009320:Atrial Natriuretic Factor; D006162:Guanylate Cyclase; D017461:Receptors, Atrial Natriuretic Factor; C091715:atrial natriuretic factor receptor A