Interaction of human gamma-carboxyglutamic acid domainless prothrombin with phospholipids

Sphingolipids as Bioactive Regulators of Thrombin Generation

Sphingolipids contribute to modulation of two opposing cell processes, cell growth and apoptotic cell death; ceramide and sphingosine promote the latter and sphingosine-1-phosphate triggers the former. Thrombin, a pro-inflammatory protease that is regulated by the blood coagulation cascade, exerts similar effects depending on cell type. Here we report a new mechanism for cross-talk between sphingolipid metabolism and thrombin generation. Sphingosine and sphinganine, but not ceramide or sphingosine-1-phosphate, down-regulated thrombin generation on platelet surfaces (IC(50) = 2.4 and 1.4 microm for sphingosine and sphinganine, respectively) as well as in whole plasma clotting assays. Thrombin generation was also inhibited by glucosylsphingosine, lysosphingomyelin, phytosphingosine, and primary alkylamines with >10 carbons. Acylation of the amino group ablated anticoagulant activities. Factor Va was required for the anticoagulant property of sphingosine because prothrombin activation was inhibited by sphingosine, sphinganine, and stearylamine in the presence but not in the absence of factor Va. Sphingosine did not inhibit thrombin generation when Gla-domainless factor Xa was used in prothrombinase assays, whereas sphingosine inhibited activation of Gla-domainless prothrombin by factor Xa/factor Va in the absence of phospholipids (IC(50) = 0.49 microm). Fluorescence spectroscopy studies showed that sphingosine binds to fluorescein-labeled factor Xa and that this interaction required the Gla domain. These results imply that sphingosine disrupts interactions between factor Va and the Gla domain of factor Xa in the prothrombinase complex. Thus, certain sphingolipids may be bioactive lipid mediators of thrombin generation such that certain sphingolipid metabolites may modulate proteases that affect cell growth and death, blood coagulation, and inflammation.

Evidence from total internal reflection fluorescence microscopy for calcium-independent binding of prothrombin to negatively charged planar phospholipid membranes

Measurements to test for a proposed Ca2+-independent interaction of prothrombin with membranes containing acidic phospholipids are described. Fluorescein-labeled bovine prothrombin and its amino- and carboxy-terminal peptides, prothrombin fragment 1 and prethrombin 1, were added at various concentrations in the presence or absence of Ca2+ to the aqueous space bathing substrate-supported planar membranes composed of 1-palmitoyl-2-oleoyl-3-sn-phosphatidylcholine (POPC), POPC/bovine brain phosphatidylserine (bovPS) (70:30 mol/mol), or POPC/1,2-dioleoyl-3-sn-phosphatidylglycerol (DOPG) (70:30 mol/mol). Total internal reflection fluorescence microscopy (TIRFM) at the membrane-solution interface showed a significant enhancement by acidic lipids of prothrombin and prothrombin fragment 1 binding in the presence of 5 mM Ca2+, with apparent dissociation constants of 0.4 and 1 microM, respectively. TIRFM measurements indicated that bovPS and DOPG also significantly enhanced the binding of fluorescein-labeled prothrombin to the planar membranes in the absence of Ca2+, with apparent dissociation constants (13-30 microM) at least an order of magnitude larger than the Ca(2+)-dependent constant for prothrombin binding. Association of prethrombin 1 but not prothrombin fragment 1 with membranes in the absence of Ca2+ was enhanced by the presence of bovPS in the membranes, which suggests that the Ca(2+)-independent binding site(s) is (are) in the prethrombin 1 but not the fragment 1 portion of prothrombin.

Interaction of phospholipids with proteins, peptides and amino acids. New advances 1987-1989

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins, peptides and amino acids. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. The effect of the interaction on the structure and biological activity of the interacting biomolecules is discussed.