Effect of acylglyceride content on the structure and function of reconstituted high density lipoprotein particles

The effects of different acylglycerides on the conformation and charge of a polipoprotein A-I (apoA-I) have been investigated in reconstituted high den sity lipoproteins (LpA-I), Various amounts of diacylglycerol (DG) and triac ylglycerol (TG) were incorporated into sonicated spherical LpA-I particles containing 2 molecules of apoA-I and 80 molecules of phospholipid, Inclusio n of 30 molecules of TG into the LpA-I particle increases the net negative charge of apoA-I (-8.5 to -9.3 mV), but has little effect on the amount and thermodynamic stability of the cr. helices in apoA-I. Incorporation of 30 molecules of DG into the lipoprotein complex promotes a small increase in t he cu-helix content and stability, but greatly increases the net negative c harge of apoA-I (-8.5 to -11.2 mV), Inclusion of DG increases the immunorea ctivity of two epitopes in the N terminus of apoA-I, but decreases the expo sure of a domain closer to the C terminus (residues 148-186) of the apoprot ein, In contrast, TG increases the exposure of epitopes over the entire apo A-I molecule; TG increases the immunoreactivity of epitopes for 13 differen t monoclonal antibodies to apoA-I, Incubations with purified lecithin:chole sterol acyltransferase show that cholesterol esterification is stimulated b y DG, but inhibited by TG. The data show that TG and DG have different effe cts on apoA-I structure and function and this suggests that the TG-to-DG ra tio in HDL may directly affect the metabolism of this lipoprotein class.