Formation of two-dimensional arrays of annexin V on phosphatidylserine-containing liposomes.
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.
Pigault
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C
Laboratoire de Biophysique, URA CNRS 491, Université Louis Pasteur de Strasbourg, Faculté de Pharmacie, Illkirch, France.
Follenius-Wund
A
A
Schmutz
M
M
Freyssinet
J M
JM
Brisson
A
A
D017304:Annexin A5 / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008051:Lipid Bilayers; D008081:Liposomes; D008854:Microscopy, Electron; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D011487:Protein Conformation
D017304:Annexin A5; D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; C017251:1,2-oleoylphosphatidylcholine; D002118:Calcium