1. Structures of apolipoprotein A-I in high density lipoprotein generated by electron microscopy and biased simulations
- Author
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Peter Gysbers, Jitka Petrlova, Hans Hebert, Caroline Jegerschöld, Stefan Wallin, Lin Zhu, and Jens O. Lagerstedt
- Subjects
0301 basic medicine ,Very low-density lipoprotein ,Protein Conformation ,Cryo-electron microscopy ,Biophysics ,Antiparallel (biochemistry) ,Biochemistry ,Protein Structure, Secondary ,03 medical and health sciences ,chemistry.chemical_compound ,Protein structure ,Humans ,Molecular Biology ,POPC ,Phospholipids ,Apolipoprotein A-I ,Chemistry ,Cholesterol ,nutritional and metabolic diseases ,Microscopy, Electron ,Crystallography ,030104 developmental biology ,Structural biology ,Phosphatidylcholines ,lipids (amino acids, peptides, and proteins) ,Lipoproteins, HDL ,Lipoprotein - Abstract
Background Apolipoprotein A-I (apoA-I) in high-density lipoprotein (HDL) is a key protein for the transport of cholesterol from the vascular wall to the liver. The formation and structure of nascent HDL, composed of apoA-I and phospholipids, is critical to this process. Methods The HDL was assembled in vitro from apoA-I, cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at a 1:4:50 molar ratio. The structure of HDL was investigated in vitreous samples, frozen at cryogenic temperatures, as well as in negatively stained samples by transmission electron microscopy. Low resolution electron density maps were next used as restraints in biased Monte Carlo simulations of apolipoprotein A-I dimers, with an initial structure derived from atomic resolution X-ray structures. Results Two final apoA-I structure models for the full-length structure of apoA-I dimer in the lipid bound conformation were generated, showing a nearly circular, flat particle with an uneven particle thickness. Conclusions The generated structures provide evidence for the discoidal, antiparallel arrangement of apoA-I in nascent HDL, and propose two preferred conformations of the flexible N-termini. General significance The novel full-length structures of apoA-I dimers deepens the understanding to the structure-function relationship of nascent HDL with significance for the prevention of lipoprotein-related disease. The biased simulation method used in this study provides a powerful and convenient modelling tool with applicability for structural studies and modelling of other proteins and protein complexes.
- Published
- 2017