Conformational Reorganisation of Apolipoprotein E Triggered by Phospholipid Assembly

Abstract

Apolipoprotein E ( ApoE) is a major determinant protein of lipid-metabolism and actively participates in lipid transport in plasma and central nervous system. As a part of its lipid-transport activity, low-density-lipid receptor (LDLR) needs to recognise apoE as a ligand. But, all prior evidences point to the fact that the recognition of apoE by LDLR only takes place in presence of lipid molecules which are assumed to play an important role in conformationally activating apoE upon binding. However, the molecular mechanism underlying the complexation process of apoE with lipid molecules and associated lipid-induced conformational change of apoE are currently elusive. Here we capture the spontaneous complexation process of monomeric apoE3 and phospholipid molecules by employing molecular dynamics simulation at multiple resolution. In particular, our multi scale simulations demonstrate a large-scale conformational change of the full-length apoE3, triggered by two-stage apoE-lipid complexation process. At first stage, lipid molecules assemble close to C-terminal domain of the protein and induce a rapid separation of C-terminal domain of monomeric apoE3 from rest of its tertiary fold. In the second and final stage, long-time scale simulation captures a slow on-the-fly lipid-induced inter-helix separation process in N-terminal domain of the protein. The resultant equilibrated complex, as obtained in the current work resembles an `open conformation' of lipid-stabilised apoE, previously hypothesised based on small-angle X-ray scattering experiments. Taken together, the simulations provide a molecular view of kinetic interplay of apoE and lipid complexation multi-stage process leading to conformational changes in protein, potentially making it conducive for recognising LDLR.