THE INFLUENCE OF CHOLESTERYL ESTER TRANSFER PROTEIN ON THE COMPOSITION, SIZE, AND STRUCTURE OF SPHERICAL, RECONSTITUTED HIGH-DENSITY-LIPOPROTEINS

The effect of cholesteryl ester transfer protein (CETP) on the size, c omposition, and structure of spherical, reconstituted HDL (rHDL) which contain apolipoprotein (ape) A-I as their sole apolipoprotein has bee n studied. Spherical rHDL were incubated with CETP and Intralipid for up to 24 h, During this time CETP promoted transfers of cholesteryl es ters (CE) and triglyceride (TG) between rHDL and Intralipid, As a resu lt, the rHDL became depleted of CE and enriched in TG, However, as the loss of CE from the rHDL was greater than the gain of TG, the concent ration of core lipids in the rHDL decreased, The decrease in the conce ntration of rHDL core lipids, which was evident throughout the incubat ion, was accompanied by a reduction in rHDL diameter from 9.2 to 8.0 n m, the dissociation of apoA-I hom rHDL and a decrease in the number of apoA-I molecules, from three/particle in the 9.2-nm rHDL, to two/part icle in the 8.0 nm rHDL, Spectroscopic studies showed that the lipid-w ater interface and phospholipid packing of the 8,0-nm rHDL were, respe ctively, more polar and less ordered than those of the 9,2-nm rHDL, Qu enching studies with KI revealed that the number of exposed apoA-I Trp residues in the 9.2- and 8,0-nm rHDL was two and three, respectively, Circular dichroism established that the 9.2- and 8,0-nm rHDL had iden tical apoA-I alpha-helical contents, The 9.2- and 8.0 nm rHDL also had identical surface charges as determined by agarose gel electrophoresi s, Denaturation studies with guanidine hydrochloride demonstrated that apoA-I is more stable in 8.0 nm rHDL than in 9,2-nm rHDL, It is concl uded that CETP converts rHDL to small, TG-enriched, apoA-I-depleted pa rticles with increased lipid-water interfacial hydration and less orde red phospholipid packing, These changes are associated with enhanced s tability and minor changes to the conformation of the apoA-I which rem ains associated with the rHDL.