title: Facilitated phosphatidylserine (PS) flip-flop and thrombin activation using a synthetic PS scramblase.
abstract: A cationic steroid with a hydrogen-bonding pocket that has an affinity for anionic phospholipid headgroups was synthesized and shown to strongly promote the translocation or flip-flop of a fluorescent, C(6)NBD-labeled phosphatidylserine probe (C(6)NBD-PS) across vesicle membranes. In addition, the synthetic PS scramblase increases the levels of endogenous PS on the surface of erythrocytes as monitored by flow cytometry analysis of annexin V-FITC binding. The PS scrambling effect is enhanced when the cells are pretreated with N-ethylmaleimide (NEM), an inhibitor of the endogenous aminophospholipid flippase. The combination of NEM and synthetic PS scramblase enhances the ability of erythrocytes to promote the conversion of prothrombin to thrombin by a factor of 4. An analogous cationic steroid with a smaller binding pocket has no measurable PS translocation activity, a result that is attributed to its inability to sufficiently diminish the hydrophilicity of the multiply charged PS headgroup.
authors.affiliation: Department of Chemistry and Biochemistry and the Walther Cancer Research Center, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: J Middleton
authors.initials: JM
authors.lastname: Boon
authors.forename: Timothy N
authors.initials: TN
authors.lastname: Lambert
authors.forename: Adam L
authors.initials: AL
authors.lastname: Sisson
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Davis
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Smith
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000737:chemistry / Q000493:pharmacokinetics; D006801:Humans; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010718:Phosphatidylserines / Q000737:chemistry / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D013917:Thrombin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D008081:Liposomes; D008565:Membrane Proteins; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D013917:Thrombin; D005033:Ethylmaleimide