title: A neutron solution scattering study of the structure of annexin-V and its binding to lipid vesicles.
abstract: Low-angle neutron solution scattering has been used to study the structure of annexin-V and its interaction with small single-bilayer vesicles consisting of phosphatidylserine and phosphatidylcholine at a 33:66 (mol:mol) ratio. There was no evidence for a change in the state of aggregation of annexin-V, which remained as a monomer in the presence of 3 mM-free calcium. The only difference between presence and absence of free calcium was the increase of the radius of gyration, from 19(+/- 0.4) A to 22(+/- 0.4) A in 2H2O buffer and from 19.7(+/- 1.2) A to 22.2(+/- 1.2) A in H2O buffer. The relative molecular weight, outer radius and average surface area per lipid of vesicles alone were respectively 2.5(+/- 0.5) x 10(6), 127 A and 90(+/- 19) A2. These parameters were not modified in the presence of free calcium, which testified to the absence of vesicle coalescence. The calcium-dependent binding of annexin-V was essentially interfacial and therefore did not alter significantly the structural characteristics of the vesicles. At saturation, 80(+/- 10) annexin-V molecules were bound per vesicle, the available area per molecule being 2500(+/- 300) A2 thus covering approximately 28 lipid head groups. The protein shell was approximately 35 A thick. The apparent dissociation constant was probably less than 1 nM. These data contribute to a more accurate definition of annexin-V as a possible probe of those cytodynamic events involving exposure of sequestered membrane aminophospholipids.
authors.affiliation: Unité 311 INSERM, Centre Régional de Transfusion Sanguine, Strasbourg, France.
authors.forename: C
authors.initials: C
authors.lastname: Ravanat
authors.forename: J
authors.initials: J
authors.lastname: Torbet
authors.forename: J M
authors.initials: JM
authors.lastname: Freyssinet
mesh_terms: D017304:Annexin A5; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D009502:Neutrons; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010920:Placenta / Q000737:chemistry; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D011487:Protein Conformation; D012542:Scattering, Radiation; D012996:Solutions / Q000737:chemistry
chemical_list: D017304:Annexin A5; D002135:Calcium-Binding Proteins; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D011257:Pregnancy Proteins; D012996:Solutions; D002118:Calcium