Membrane-bound calmodulin in Xenopus laevis oocytes as a novel binding site for melatonin

FASEB J. 1998 Oct;12(13):1401-8. doi: 10.1096/fasebj.12.13.1401.

Abstract

Melatonin has been suggested as a physiological antagonist of calmodulin. In this work, we have characterized melatonin binding sites in Xenopus laevis oocyte membranes. Binding of [125I]melatonin by X. laevis oocyte membranes fulfills all criteria for binding to a receptor site. Binding was dependent on time, temperature, and membrane concentration and was stable, reversible, saturable, and specific. The binding site was also pharmacologically characterized. Stoichiometric studies showed a high-affinity binding site with a Kd of 1.18 nM. These data are in close agreement with data obtained from kinetic studies (Kd=0.12 nM). In competition studies, we observed a low-affinity binding site (Kd=63.41 microM). Moreover, the binding site was characterized as calmodulin. Thus, binding was dependent on calcium and blocked by anti-CaM antibodies in a concentration-dependent manner. Calmodulin inhibitor chlorpromazine also inhibited binding of the tracer. From these results, it is suggested that membrane-bound calmodulin acts as a melatonin binding site in Xenopus laevis oocytes, where it might couple cellular activities to rhythmic circulating levels of melatonin. This hypothesis correlates with the previous findings describing melatonin as a physiological antagonist of calmodulin.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Binding, Competitive
  • Calcium / physiology
  • Calcium Signaling / physiology*
  • Calmodulin / antagonists & inhibitors
  • Calmodulin / metabolism*
  • Chlorpromazine / pharmacology
  • Egg Proteins / metabolism*
  • Female
  • Indoles / metabolism
  • Kinetics
  • Melatonin / metabolism*
  • Membrane Proteins / metabolism*
  • Oocytes / metabolism*
  • Protein Binding
  • Receptors, Cell Surface / metabolism*
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Melatonin
  • Temperature
  • Xenopus laevis

Substances

  • Calmodulin
  • Egg Proteins
  • Indoles
  • Membrane Proteins
  • Receptors, Cell Surface
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Melatonin
  • Melatonin
  • Calcium
  • Chlorpromazine