Co-operative regulation of ligand binding to melanocortin receptor subtypes : evidence for interacting binding sites

• This study evaluates the binding the melanocyte stimulating hormone peptide analogue [125I]NDP-MSH to melanocortin receptors MC1, MC3, MC4 and MC5 in insect cell membranes produced by baculovirus expression systems. The presence of Ca2+ was found to be mandatory to achieve specific [125I]NDP-MSH binding to the melanocortin receptors. Although association kinetics of [125I]NDP-MSH followed the regularities of simple bimolecular reactions, the dissociation of [125I]NDP-MSH from the melanocortin receptors was heterogeneous. Eleven linear and cyclic MSH peptides studied displaced the [125I]NDP-MSH binding to the studied melanocortin receptors, with the shapes of their competition curves varying from biphasic or shallow to super-steep (Hill coefficients ranging from 0.4 to 1.5). Notably the same peptide often gave highly different patterns on different melanocortin receptor subtypes; e.g. the MC4 receptor selective antagonist HS131 gave a Hill coefficient of 1.5 on the MC1 receptor but 0.5-0.7 on the MC(3-5) receptors. Adding a mask of one of the peptides to block its high affinity binding did not prevent other competing peptides to yield biphasic competition curves. The data indicate that the binding of MSH peptides to melanocortin receptors are governed by a complex dynamic homotropic co-operative regulations.

Subject headings

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Farmaceutiska vetenskaper (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Pharmaceutical Sciences (hsv//eng)

Keyword

Animals

Binding Sites

Binding; Competitive/drug effects

Calcium/pharmacology

Cell Line

Cell Line; Tumor

Cell Membrane/metabolism

Comparative Study

Dose-Response Relationship; Drug

Iodine Radioisotopes

Kinetics

Ligands

Melanoma; Experimental/metabolism/pathology

Peptides; Cyclic/metabolism/pharmacology

Radioligand Assay

Receptor; Melanocortin; Type 1/metabolism

Receptor; Melanocortin; Type 3/metabolism

Receptor; Melanocortin; Type 4/metabolism

Receptors; Melanocortin/*metabolism

Research Support; Non-U.S. Gov't

Spodoptera

Time Factors

alpha-MSH/*analogs & derivatives/metabolism

gamma-MSH/metabolism/pharmacology

PHARMACY

FARMACI

Publication and Content Type

ref (subject category)

art (subject category)