title: Modulation of prothrombinase assembly and activity by phosphatidylethanolamine.
abstract: Constituents of platelet membranes regulate the activity of the prothrombinase complex. We demonstrate that membranes containing phosphatidylcholine and phosphatidylethanolamine (PE) bind factor Va with high affinity (K(d) = ∼10 nm) in the absence of phosphatidylserine (PS). These membranes support formation of a 60-70% functional prothrombinase complex at saturating factor Va concentrations. Although reduced interfacial packing does contribute to factor Va binding in the absence of PS, it does not correlate with the enhanced activity of the Xa-Va complex assembled on PE-containing membranes. Instead, specific protein-PE interactions appear to contribute to the effects of PE. In support of this, soluble C6PE binds to recombinant factor Va(2) (K(d) = ∼6.5 μm) and to factor Xa (K(d) = ∼91 μm). C6PE and C6PS binding sites of factor Xa are specific, distinct, and linked, because binding of one lipid enhances the binding and activity effects of the other. C6PE triggers assembly (K(d)(app) = ∼40 nm) of a partially active prothrombinase complex between factor Xa and factor Va(2), compared with K(d)(app) for C6PS ∼2 nm. These findings provide new insights into the possible synergistic roles of platelet PE and PS in regulating thrombin formation, particularly when exposed membrane PS may be limiting.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7260. Electronic address: rinku-majumder@med.unc.edu.
authors.forename: Rinku
authors.initials: R
authors.lastname: Majumder
authors.affiliation: Division of Hematology, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27702-3656.
authors.forename: Xiaoe
authors.initials: X
authors.lastname: Liang
authors.affiliation: Division of Hematology, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27702-3656.
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Quinn-Allen
authors.affiliation: Division of Hematology, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27702-3656. Electronic address: william.kane@duke.edu.
authors.forename: William H
authors.initials: WH
authors.lastname: Kane
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7260. Electronic address: uncbrl@med.unc.edu.
authors.forename: Barry R
authors.initials: BR
authors.lastname: Lentz
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D005165:Factor V / Q000737:chemistry* / Q000378:metabolism; D015943:Factor Va / Q000737:chemistry*; D015951:Factor Xa / Q000737:chemistry* / Q000378:metabolism; D008567:Membranes, Artificial; D010714:Phosphatidylethanolamines / Q000737:chemistry* / Q000378:metabolism; D013917:Thrombin / Q000737:chemistry / Q000378:metabolism
chemical_list: D008567:Membranes, Artificial; D010714:Phosphatidylethanolamines; C022475:prothrombinase complex; C483858:phosphatidylethanolamine; D015943:Factor Va; D005165:Factor V; D013917:Thrombin; D015951:Factor Xa