Calcium-dependent and calcium-independent interactions of prothrombin fragment 1 with phosphatidylglycerol/phosphatidylcholine unilamellar vesicles

Abstract

We have measured the phase behavior of mixed dipentadecanoylphosphatidylglycerol (DC15PG)/dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles (SUV) in the presence of saturating (greater than 98% occupancy of binding sites) concentrations of bovine prothrombin fragment 1 and 5 mM Ca2+. Binding of fragment 1 in the presence of Ca2+ was verified by an increase in 90 degrees light scattering. Only in the cases of DC15PG/DMPC SUV below their phase transition and of pure DMPC SUV were such light scattering measurements not reversible upon addition of ethylenediaminetetraacetic acid to complex Ca2+. Phase-behavior changes of DC15PG/DMPC SUV as monitored by diphenylhexatriene fluorescence anisotropy occurred in concert with the binding of fragment 1. The major effects of peptide binding on SUV phase behavior were to raise the phase-transition temperature by 2-15 degrees C, depending on vesicle composition, and, in general, to make the phase diagram for these small vesicles closely resemble that of large vesicles. No evidence was obtained for the existence of lateral membrane domains with distinct compositions induced by the binding of prothrombin fragment 1 plus Ca2+. Surprisingly, fragment 1 without Ca2+ also altered the phase behavior of DC15PG/DMPC SUV. Most striking was the effect of fragment 1 (with or without Ca2+) on DMPC SUV phase behavior. Freeze-fracture electron microscopy demonstrated that pure DMPC vesicles were induced to fuse in the presence of fragment 1, while vesicles containing DC15PG remained intact. The rate of DMPC SUV fusion (followed by 90 degrees light scattering) increased with increasing fragment 1 concentration but was not saturable up to 40 microM fragment 1, suggesting a weak, nonspecific interaction between fragment 1 and the neutral phospholipid vesicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct Enthalpy Measurements of Factor X and Prothrombin Association with Small and Large Unilamellar Vesicles

“…Such changes in phospholipid packing upon prothrombin fragment 1 binding have been suggested (Lentz et al, 1985). However, the latter changes were observed without calcium present and may not be related.…”

The ω-Loop Region of the Human Prothrombin γ-Carboxyglutamic Acid Domain Penetrates Anionic Phospholipid Membranes

“…In control experiments we measured the light scattering effects of these phospholipid vesicles on a reference fluorophore, L-tryptophan (33). This is of particular importance when measuring fluorescence in the presence of 100% PC vesicles, which are prone to aggregation (36). The addition of 100% PC vesicles resulted in a 20 -30% decrease in both the fluorescence of the peptide and reference sample (data not shown).…”

Insights into the complex association of bovine factor Va with acidic-lipid-containing synthetic membranes

“…This acidic lipid domain model was originally proposed for cytochrome c binding to mixed cardiolipin/spin-labeled cholesterol membranes (Birrell and Griffith, 1976) and then applied to the binding of several extrinsic proteins, including prothrombin (Lim et al, 1977;Mayer and Nelsestuen, 1981) and factors Xa and Va (Bloom et al, 1979;Nelsestuen, 1981, 1983; Pusey et al, 1982). The domain or cluster model of extrinsic protein interaction has been questioned even for cytochrome c (Reitveld et al, 1986) and has also been challenged with regard to the prothrombinase components (Lentz et al, 1985;Jones and Lentz, 1986;van de Waart et al, 1987;Tendian and Lentz, 1990;Bazzi and Nelsestuen, 1991).…”