Submicellar bile salts stimulate phosphatidylcholine transfer activity of sterol carrier protein 2

Abstract

To explore a potential role for sterol carrier protein 2 (SCP2, also known as non-specific lipid transfer protein) in hepatocellular phospholipid trafficking, we examined the influence of submicellar bile salt concentrations on phosphatidylcholine (PC) transfer activity of SCP2. We measured rate constants for first-order transfer of sn -1 palmitoyl, sn -2 parinaroyl PC, a naturally fluorescent selfquenching phospholipid between model membranes. Purified bovine liver SCP2 promoted transfer of PC from donor to acceptor small unilamellar vesicles. Taurine-and glycine-conjugated bile salts (anionic steroid detergent-like molecules), at concentrations well below their critical micellar concentrations, stimulated PC transfer activity of SCP2 80-to 140-fold. Rate constants increased in proportion to bile salt concentration, temperature, and bile saltmembrane binding affinity. Sodium taurofusidate, a conjugated fungal bile salt analog, also activated PC transfer whereas no effect was observed with the anionic and nonionic straight chain detergents sodium dodecyl sulfate and octylglucoside, respectively. Thermodynamic and kinetic analyses of PC transfer support a mechanism in which bile salts stimulate SCP2 activity by partitioning into donor vesicles and enhancing membrane association of SCP2. These results imply that under physiological conditions, SCP2 may contribute to hepatocellular selection and transport of biliary PCs.-Leonard, A. N., and D. E. Cohen. Submicellar bile salts stimulate phosphatidylcholine transfer activity of sterol carrier protein 2.

Intestinal lipid absorption and transport

“…Additionally, SCP-2 is involved in the intracellular transport of cholesterol from cytoplasmic lipid droplets to mitochondria and the translocation of cholesterol from the outer mitochondrial membrane to the inner mitochondrial membrane (188). It also appears to be involved in the intracellular trafficking of PC (189,190) and FAs (191), and SCP-2 has been proposed to play a role in peroxisomal FA-CoA binding (192).…”