Formation of two-dimensional arrays of annexin V on phosphatidylserine-containing liposomes

J Mol Biol. 1994 Feb 11;236(1):199-208. doi: 10.1006/jmbi.1994.1129.

Abstract

Annexins are intracellular proteins which bind to membranes in a Ca(2+)-dependent manner and which have been proposed to play regulatory roles in different membrane processes. In the present study, the stoichiometry of the Ca(2+)-dependent binding of annexin V to phosphatidylserine molecules incorporated into liposomes was studied by fluorescence spectroscopy. The Ca(2+)-dependence of the binding was determined using liposomes made of dioleoylphosphatidylserine (PS) and dioleoylphosphatidylcholine (PC), with a PC/PS molar ratio ranging from 1 to 800. These liposomes were shown to be mostly unilamellar by cryoelectron microscopy. [Ca2+]1/2 concentrations required for half-maximal binding of annexin V range from 57 microM at PC/PS = 1 up to 96 mM at PC/PS = 800. Titration of accessible PS molecules showed that annexin V molecules bind equally well to liposomes of PC/PS ratio ranging from 1 to 400. The stoichiometry of the binding between annexin V and PS, determined at low PS content, is eight annexin V molecules per one PS molecule. We propose a novel model of the Ca(2+)-dependent interaction between annexin V and lipid membranes, based on the formation of two-dimensional arrays of annexin V molecules, stabilized by both protein-lipid and protein-protein interactions.

Publication types

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

MeSH terms

  • Annexin A5 / chemistry*
  • Annexin A5 / isolation & purification
  • Annexin A5 / metabolism
  • Calcium / pharmacology
  • Female
  • Humans
  • Kinetics
  • Lipid Bilayers
  • Liposomes*
  • Microscopy, Electron
  • Phosphatidylcholines
  • Phosphatidylserines*
  • Placenta / metabolism
  • Pregnancy
  • Protein Conformation*

Substances

  • Annexin A5
  • Lipid Bilayers
  • Liposomes
  • Phosphatidylcholines
  • Phosphatidylserines
  • 1,2-oleoylphosphatidylcholine
  • Calcium