In vitro binding of synthetic acylated lipid-associating peptides to high-density lipoproteins: effect of hydrophobicity

Publisher Website
Google Scholar
Abstract
To measure the effect of hydrophobicity on the binding of model apoproteins to lipoproteins, a 15 amino acid lipid-associating peptide (LAP) with acyl chains of various lengths (0-18 carbons) bound to the N-terminal amino acid through a peptide bond was synthesized. The acylated LAP preferentially bound to [human plasma] to high-density lipoprotein (HDL) and were activators of lecithin:cholesterol acyltransferase. Circular dichroic spectra indicated that the LAP association with phospholipid was accompanied by increased .alpha.-helical structure. The LAP self-associated in solution as judged from tryptophan fluorescence analysis. These characteristics, which are comparable to those of apolipoprotein A-I, were strongly dependent upon the acyl chain length of the LAP. The equilibrium constants (Keq) for the association of LAP to reassembled HDL were measured by equilibrium dialysis at several temperatures. At 37.degree. C, Keq increased by 3 orders of magnitude as the number of carbon units was increased from 0 to 16; there was a log-linear relationship between Keq and the acyl chain length. The free energy of association (.DELTA.Ga) decreased by a constant value for each methylene unit added to the acyl chain (0.35 kcal mol-1), clearly demonstrating a strict hydrophobic effect. This change of .DELTA.Ga was enthalpy rather than entropy driven. With all other parameters including putative .alpha.-helicity, sequence and MW being constant, the binding of a lipid-associating peptide to lipoprotein is governed by its hydrophobicity.