Influence of ApoA-I structure on the ABCA1-mediated efflux of cellular lipids

Academic Article

Abstract

  • The influence of apolipoprotein (apo) A-I structure on ABCA1-mediated efflux of cellular unesterified (free) cholesterol (FC) and phospholipid (PL) is not well understood. To address this issue, we used a series of apoA-I mutants to examine the contributions of various domains in the molecule to ABCA1-mediated FC and PL efflux from mouse J774 macrophages and human skin fibroblasts. Irrespective of the cell type, deletion or disruption of the C-terminal lipid-binding domain of apoA-I drastically reduced the FC and PL efflux (∼90%), indicating that the C-terminal amphipathic α-helix is required for high affinity microsolubilization of FC and PL. Deletion in the N-terminal region of apoA-I also reduced the lipid efflux (∼30%) and increased the Km about 2-fold compared with wild type apoA-I, whereas deletion of the central domain (Δ123-166) had no effect on either K m or Vmax. These results indicate that ABCA1-mediated lipid efflux is relatively insensitive to the organization of the apoA-I N-terminal helix-bundle domain. Alterations in apoA-I structure caused parallel changes in its ability to bind to a PL bilayer and to induce efflux of FC and PL. Overall, these results are consistent with a two-step model for ABCA1-mediated lipid efflux. In the first step, apoA-I binds to ABCA1 and hydrophobic α-helices in the C-terminal domain of apoA-I insert into the region of the perturbed PL bilayer created by the PL transport activity of ABCA1, thereby allowing the second step of lipidation of apoA-I and formation of nascent high density lipoprotein particles to occur.
  • Published In

    Digital Object Identifier (doi)

    Author List

  • Vedhachalam C; Liu L; Nickel M; Dhanasekaran P; Anantharamaiah GM; Lund-Katz S; Rothblat GH; Phillips MC
  • Start Page

  • 49931
  • End Page

  • 49939
  • Volume

  • 279
  • Issue

  • 48