Structure and intermolecular interactions in spheroidal high-density lipoprotein subpopulations

Chris J Malajczuk; Neha S Gandhi; Ricardo L Mancera

doi:10.1016/j.yjsbx.2020.100042

Structure and intermolecular interactions in spheroidal high-density lipoprotein subpopulations

J Struct Biol X. 2020 Dec 10:5:100042. doi: 10.1016/j.yjsbx.2020.100042. eCollection 2021.

Authors

Chris J Malajczuk¹, Neha S Gandhi², Ricardo L Mancera¹

Affiliations

¹ School of Pharmacy and Biomedical Sciences, Curtin Health Innovation Research Institute and Curtin Institute for Computation, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
² School of Mathematical Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, QLD 4000, Australia.

Abstract

Human serum high-density lipoproteins (HDLs) are a population of small, dense protein-lipid aggregates that are crucial for intravascular lipid trafficking and are protective against cardiovascular disease. The spheroidal HDL subfraction can be separated by size and density into five major subpopulations with distinct molecular compositions and unique biological functionalities: HDL_3c, HDL_3b, HDL_3a, HDL_2a and HDL_2b. Representative molecular models of these five subpopulations were developed and characterised for the first time in the presence of multiple copies of its primary protein component apolipoprotein A-I (apoA-I) using coarse-grained molecular dynamics simulations. Each HDL model exhibited size, morphological and compositional profiles consistent with experimental observables. With increasing particle size the separation of core and surface molecules became progressively more defined, resulting in enhanced core lipid mixing, reduced core lipid exposure at the surface, and the formation of an interstitial region between core and surface molecules in HDL_2b. Cholesterol molecules tended to localise around the central helix-5 of apoA-I, whilst triglyceride molecules predominantly interacted with aromatic, hydrophobic residues located within the terminal helix-10 across all subpopulation models. The three intermediate HDL models exhibited similar surface profiles despite having distinct molecular compositions. ApoA-I in trefoil, quatrefoil and pentafoil arrangements across the surface of HDL particles exhibited significant warping and twisting, but largely retained intermolecular contacts between adjacent apoA-I chains. Representative HDL subpopulations differed in particle size, morphology, intermolecular interaction profiles and lipid and protein dynamics. These findings reveal how different HDL subpopulations might exhibit distinct functional associations depending on particle size, form and composition.

Keywords: Coarse-grained; HDL subpopulation; High-density lipoprotein; Molecular dynamics simulation; apolipoprotein A-I.