title: Structure of membrane-bound human factor Va.
abstract: Coagulation factor Va is an essential cofactor which combines with the serine protease factor Xa on a phospholipid surface to form the prothrombinase complex. In the present study, the structure of factor Va interacting with lipid surfaces containing phosphatidylserine was studied by electron microscopy. Two-dimensional crystals of factor Va were obtained on planar lipid films under quasi-physiological conditions. The two-dimensional projected structure of factor Va was calculated at a resolution of 2 nm, revealing dimers of factor Va arranged on the surface lattice with the symmetry of the plane group p2. Average unit cell dimensions are a = 14.4 nm, b = 8.8 nm, gamma = 107 degrees. Each factor Va molecule presents two distinct domains of protein density consisting of one small domain, of 3 nm in diameter, connected to a larger domain of about 6 nm x 4.5 nm. The projected structure of factor Va covers an area equivalent to about fifty phospholipid molecules. In addition, edge-on views of factor Va molecules bound to liposomes reveal a globular structure connected through a thin stem to the liposome surface. A three-dimensional model of membrane-bound factor Va is proposed.
authors.affiliation: Laboratoire de Génétique Moléculaire des Eucaryotes, CNRS, Unité 184 de Biologie Moléculaire et de Génie Génétique, INSERM, Faculté de Médecine, Strasburg, France.
authors.forename: S
authors.initials: S
authors.lastname: Stoylova
authors.forename: K G
authors.initials: KG
authors.lastname: Mann
authors.forename: A
authors.initials: A
authors.lastname: Brisson
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D003460:Crystallization; D015943:Factor Va / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D008081:Liposomes; D008854:Microscopy, Electron; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D008081:Liposomes; D015943:Factor Va