title: Incorporation of blood clotting factor X into phospholipid model membranes: fluorescence microscopy imaging and subphase effects surrounding the lipid phase transition region.
abstract: Factor X is a blood clotting protein that associates at membrane surfaces to become activated during the coagulation cascade. A molecular level understanding of the protein-membrane phospholipid interactions has not been reached, although it is thought that the protein binds to phospholipids in the presence of calcium through a bridge with the Gla (gamma-carboxyglutamic acid) domain on the protein. In this work, phospholipid Langmuir monolayers have been utilized as model membranes to study factor X association with phospholipid membrane components. Surface pressure measurements indicate that subphase addition of sodium, magnesium, and calcium ions enhances protein penetration of the lipid monolayer, with the largest association found with calcium ions in the subphase. Fluorescence microscopy images collected after protein penetration of lipid monolayers indicate monolayer condensation in the presence of sodium and magnesium ions. Aggregation of lipid domains is induced when calcium is in the subphase, indicating binding-induced flocculation of surface lipid aggregates. Calcium binding to factor X likely causes a conformational change which allows protein-membrane interaction via hydrophobic association with lipid molecules.
authors: Department of Chemistry, Saint Louis University, 3501 Laclede Avenue, St. Louis, MO 63103-2010, USA.
authors: Jeffrey
authors: J
authors: Craft
authors: Kimberly
authors: K
authors: Epps
authors: Sam
authors: S
authors: Brancato
authors: Alexa
authors: A
authors: Serfis
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry* / Q000378:metabolism; D001777:Blood Coagulation; D001779:Blood Coagulation Factors; D002118:Calcium / Q000378:metabolism; D005170:Factor X / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D008566:Membranes / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D008954:Models, Biological
chemical_list: D001779:Blood Coagulation Factors; D008051:Lipid Bilayers; D015060:1,2-Dipalmitoylphosphatidylcholine; D005170:Factor X; D002118:Calcium