title: Three-dimensional cryoEM reconstruction of native LDL particles to 16Å resolution at physiological body temperature.
abstract: BACKGROUND
  Low-density lipoprotein (LDL) particles, the major carriers of cholesterol in the human circulation, have a key role in cholesterol physiology and in the development of atherosclerosis. The most prominent structural components in LDL are the core-forming cholesteryl esters (CE) and the particle-encircling single copy of a huge, non-exchangeable protein, the apolipoprotein B-100 (apoB-100). The shape of native LDL particles and the conformation of native apoB-100 on the particles remain incompletely characterized at the physiological human body temperature (37 °C).
  
  
  RESULTS
  To study native LDL particles, we applied cryo-electron microscopy to calculate 3D reconstructions of LDL particles in their hydrated state. Images of the particles vitrified at 6 °C and 37 °C resulted in reconstructions at ~16 Å resolution at both temperatures. 3D variance map analysis revealed rigid and flexible domains of lipids and apoB-100 at both temperatures. The reconstructions showed less variability at 6 °C than at 37 °C, which reflected increased order of the core CE molecules, rather than decreased mobility of the apoB-100. Compact molecular packing of the core and order in a lipid-binding domain of apoB-100 were observed at 6 °C, but not at 37 °C. At 37 °C we were able to highlight features in the LDL particles that are not clearly separable in 3D maps at 6 °C. Segmentation of apoB-100 density, fitting of lipovitellin X-ray structure, and antibody mapping, jointly revealed the approximate locations of the individual domains of apoB-100 on the surface of native LDL particles.
  
  
  CONCLUSIONS
  Our study provides molecular background for further understanding of the link between structure and function of native LDL particles at physiological body temperature.
authors.affiliation: Department of Biomedical Engineering and Computational Science, School of Science and Technology, Centre of Excellence in Computational Complex Systems Research, Aalto University Aalto, Finland.
authors.forename: Vibhor
authors.initials: V
authors.lastname: Kumar
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Butcher
authors.forename: Katariina
authors.initials: K
authors.lastname: Öörni
authors.forename: Peter
authors.initials: P
authors.lastname: Engelhardt
authors.forename: Jukka
authors.initials: J
authors.lastname: Heikkonen
authors.forename: Kimmo
authors.initials: K
authors.lastname: Kaski
authors.forename: Mika
authors.initials: M
authors.lastname: Ala-Korpela
authors.forename: Petri T
authors.initials: PT
authors.lastname: Kovanen
mesh_terms: D001831:Body Temperature; D020285:Cryoelectron Microscopy / Q000379:methods*; D006801:Humans; D008077:Lipoproteins, LDL / Q000648:ultrastructure*
chemical_list: D008077:Lipoproteins, LDL