Intermembrane cholesterol transfer: Role of sterol carrier proteins and phosphatidylserine

The effect of phosphatidylserine and sterol carrier proteins on cholesterol exchange was determined using an assay not requiring separation of donor and acceptor membrane vesicles. Sterol carrier protein-2 (SCP₂, also called nonspecific lipid transfer protein), but not fatty acid binding protein (FABP, also called sterol carrier protein), enhanced the initial rate of sterol exchange between neutral zwitterionic phosphatidylcholine small unilamellar vesicles (SUV) 2.3-fold. Phosphatidylserine at 10 mol% increased the initial rate of spontaneous and of SCP₂-mediated (but not FABP-mediated) sterol exchange by 22% and 44-fold, respectively. The SCP₂ potentiation of sterol transfer was dependent on SCP₂ concentration and on phosphatidylserine concentration. The SCP₂-mediated sterol transfer was inhibited by a variety of cations including KCl, divalent metal ions, and neomycin. The data suggest that SCP₂ increase in activity for sterol transfer may be partly ascribed to charge on the phospholipid. A portion of this work was presented as an abstract: Nemecz, G., Butko, P., and Schroeder, f. (1989)Biophysical Journal 55, 137a.