Mouse acyl-CoA binding protein: Effect on acyl-CoA utilization by microsomal acyl-CoA:cholesterol acyltransferase and membrane interactions

Mouse recombinant ACBP (mrACBP) was expressed in E. coli and purified. The mass and peptide sequence of mrACBP containing the native mouse ACBP amino acid sequence were confirmed by matrix assisted laser desorption time of flight (MALDI-TOF) mass spectroscopy and peptide sequencing. The mrACBP was functionally active as shown by 3.2-fold stimulation of microsomal glycerol-3-phosphate synthesis and protection of oleoyl-CoA from microsomal acyl-CoA hydrolase.; To establish the role of fatty acyl-CoA binding proteins in ACAT stimulation, independent of their ability to bind/transfer cholesterol, the effects of acyl-CoA binding protein (ACBP), which exclusively binds fatty acyl-CoAs, were compared to those of sterol carrier protein-2 (SCP-2), liver fatty acid binding protein (L-FABP), and bovine serum albumin (BSA). All of which bind cholesterol. In the presence of exogenous cholesterol, mrACBP significantly stimulated rat liver microsomal ACAT. Comparing to these fatty acyl-CoA binding proteins, the ability of mrACBP to stimulate microsomal ACAT had no correlation with the ability to transfer cholesterol. Thus, the ability of a fatty acyl-CoA binding protein to stimulate microsomal ACAT was independent of its cholesterol binding ability. In the absence of an exogenous cholesterol donor, all three intracellular fatty acyl-CoA binding proteins inhibited microsomal ACAT. These findings suggested that intracellular fatty acyl-CoA binding proteins such as ACBP differentially modulate the activity of microsomal ACAT to form cholesteryl esters, independent of cholesterol binding/transfer ability.; Although acyl-CoA binding protein (ACBP) enhances utilization of long chain fatty acyl-CoA by membrane acyltransferases, it is not known whether this occurs by direct membrane interaction. Circular dichroism (CD) and membrane filtration assay showed for the first time that ACBP directly and preferentially bound to anionic phospholipid-rich, highly-curved membranes, which induced an 8% increase in total α-helix content and facilitated transfer of fatty-acyl-CoA between mrACBP and membranes. Data suggest that both the electrostatic interaction and the membrane surface curvature may be important for mrACBP to bind membrane and transfer LCFACoA. The conformational change induced by membrane binding may reduce the affinity between mrACBP and LCFACoA and thereby affect the oleoyl-CoA transfer and extraction activities.