Lipid protein interactions in high density lipoproteins

Abstract

Delipidated high density lipoprotein (apoHDL), isolated apolipoproteins apoA I and apoA II, S carboxymethylated apoA II, apoC III, the NH2 and COOH terminal CNBr peptides of apoA II, and the COOH terminal CNBr peptide of apoA I were recombined in vitro with [N C3H3 choline]phosphatidylcholine (PC) and [N 14CH3 choline]sphingomyelin (SPM). The lipid protein complexes were analyzed by ultracentrifugal flotation, agarose gel chromatography and circular dichroism. ApoHDL, apoA II, and S carboxymethylated apoA II readily recombined with PC or SPM to form particles that were similar in size to native HDL. The COOH but not the NH2 terminal CNBr peptide of apoA II recombined with lipid. ApoA I and the COOH terminal CNBr peptide of apoA I, however, recombined with PC or SPM to only a limited extent, suggesting that protein protein interactions between apoA I and apoA II are important in the integration of apoA I into recombined lipoprotein particles. Analysis of the recombined lipid protein complexes by circular dichroism indicated that there was an increase in helical structure concomitant with lipid protein binding. The reconstituted particles had many of the physical and chemical properties of the native lipoprotein.