title: Coagulation factors bound to procoagulant platelets concentrate in cap structures to promote clotting.
abstract: Binding of coagulation factors to phosphatidylserine (PS)-exposing procoagulant-activated platelets followed by formation of the membrane-dependent enzyme complexes is critical for blood coagulation. Procoagulant platelets formed upon strong platelet stimulation, usually with thrombin plus collagen, are large "balloons" with a small (∼1 μm radius) "cap"-like convex region that is enriched with adhesive proteins. Spatial distribution of blood coagulation factors on the surface of procoagulant platelets was investigated using confocal microscopy. All of them, including factors IXa (FIXa), FXa/FX, FVa, FVIII, prothrombin, and PS-sensitive marker Annexin V were distributed nonhomogeneously: they were primarily localized in the "cap," where their mean concentration was by at least an order of magnitude, higher than on the "balloon." Assembly of intrinsic tenase on liposomes with various PS densities while keeping the PS content constant demonstrated that such enrichment can accelerate this reaction by 2 orders of magnitude. The mechanisms of such acceleration were investigated using a 3-dimensional computer simulation model of intrinsic tenase based on these data. Transmission electron microscopy and focal ion beam-scanning electron microscopy with Annexin V immunogold-labeling revealed a complex organization of the "caps." In platelet thrombi formed in whole blood on collagen under arterial shear conditions, ubiquitous "caps" with increased Annexin V, FX, and FXa binding were observed, indicating relevance of this mechanism for surface-attached platelets under physiological flow. These results reveal an essential heterogeneity in the surface distribution of major coagulation factors on the surface of procoagulant platelets and suggest its importance in promoting membrane-dependent coagulation reactions.
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia;
authors.forename: Nadezhda A
authors.initials: NA
authors.lastname: Podoplelova
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Moscow, Russia; Faculty of Physics, Moscow State University, Moscow, Russia;
authors.forename: Anastasia N
authors.initials: AN
authors.lastname: Sveshnikova
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Moscow, Russia;
authors.forename: Yana N
authors.initials: YN
authors.lastname: Kotova
authors.affiliation: Unité Mixte de Recherche-S949, INSERM, Etablissement Français du Sang-Alsace Lorraine Champagne Ardenne, Université de Strasbourg, Fédération de Médecine Translationnelle de Strasbourg, Strasbourg Cedex, France;
authors.forename: Anita
authors.initials: A
authors.lastname: Eckly
authors.affiliation: Unité Mixte de Recherche-S949, INSERM, Etablissement Français du Sang-Alsace Lorraine Champagne Ardenne, Université de Strasbourg, Fédération de Médecine Translationnelle de Strasbourg, Strasbourg Cedex, France;
authors.forename: Nicolas
authors.initials: N
authors.lastname: Receveur
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia; Faculty of Physics, Moscow State University, Moscow, Russia;
authors.forename: Dmitry Yu
authors.initials: DY
authors.lastname: Nechipurenko
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Moscow, Russia;
authors.forename: Sergey I
authors.initials: SI
authors.lastname: Obydennyi
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia; and.
authors.forename: Igor I
authors.initials: II
authors.lastname: Kireev
authors.affiliation: Unité Mixte de Recherche-S949, INSERM, Etablissement Français du Sang-Alsace Lorraine Champagne Ardenne, Université de Strasbourg, Fédération de Médecine Translationnelle de Strasbourg, Strasbourg Cedex, France;
authors.forename: Christian
authors.initials: C
authors.lastname: Gachet
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Moscow, Russia; Faculty of Physics, Moscow State University, Moscow, Russia;
authors.forename: Fazly I
authors.initials: FI
authors.lastname: Ataullakhanov
authors.affiliation: Unité Mixte de Recherche-S949, INSERM, Etablissement Français du Sang-Alsace Lorraine Champagne Ardenne, Université de Strasbourg, Fédération de Médecine Translationnelle de Strasbourg, Strasbourg Cedex, France;
authors.forename: Pierre H
authors.initials: PH
authors.lastname: Mangin
authors.affiliation: Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, Moscow, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Moscow, Russia; Faculty of Physics, Moscow State University, Moscow, Russia; Faculty of Biological and Medical Physics, Moscow Institute of Physics and Technology, Dolgoprudny, Russia.
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Panteleev
mesh_terms: D000328:Adult; D017304:Annexin A5 / Q000378:metabolism; D001777:Blood Coagulation / Q000502:physiology*; D001779:Blood Coagulation Factors / Q000378:metabolism*; D001792:Blood Platelets / Q000378:metabolism* / Q000648:ultrastructure; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D003198:Computer Simulation; D006801:Humans; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D010718:Phosphatidylserines / Q000097:blood; D015539:Platelet Activation / Q000502:physiology; D011485:Protein Binding; D013917:Thrombin / Q000378:metabolism; D013927:Thrombosis / Q000378:metabolism / Q000473:pathology
chemical_list: D017304:Annexin A5; D001779:Blood Coagulation Factors; D010718:Phosphatidylserines; D013917:Thrombin