Limits...
Polyhedral 3D structure of human plasma very low density lipoproteins by individual particle cryo-electron tomography 1 [S]

View Article: PubMed Central - PubMed

ABSTRACT

Human VLDLs assembled in the liver and secreted into the circulation supply energy to peripheral tissues. VLDL lipolysis yields atherogenic LDLs and VLDL remnants that strongly correlate with CVD. Although the composition of VLDL particles has been well-characterized, their 3D structure is elusive because of their variations in size, heterogeneity in composition, structural flexibility, and mobility in solution. Here, we employed cryo-electron microscopy and individual-particle electron tomography to study the 3D structure of individual VLDL particles (without averaging) at both below and above their lipid phase transition temperatures. The 3D reconstructions of VLDL and VLDL bound to antibodies revealed an unexpected polyhedral shape, in contrast to the generally accepted model of a spherical emulsion-like particle. The smaller curvature of surface lipids compared with HDL may also reduce surface hydrophobicity, resulting in lower binding affinity to the hydrophobic distal end of the N-terminal β-barrel domain of cholesteryl ester transfer protein (CETP) compared with HDL. The directional binding of CETP to HDL and VLDL may explain the function of CETP in transferring TGs and cholesteryl esters between these particles. This first visualization of the 3D structure of VLDL could improve our understanding of the role of VLDL in atherogenesis.

No MeSH data available.


The 2D images of negative-staining and frozen VLDL complex with mAB012. A: Survey view of a negative-staining VLDL and mAB012 mixture. B: Representative VLDL particles bound with an antibody. C: Zoomed-in view of (B) showing the antibody details. D: A field of view of the same VLDL and mAB012 mixture except that this shows a frozen hydrated sample that used the cryo-EM plunge-freezing technique. E: Representative VLDL particles bound by an antibody. F: Zoomed-in view of (E) showing the antibody details. Scale bars, 50 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC5036368&req=5

f3: The 2D images of negative-staining and frozen VLDL complex with mAB012. A: Survey view of a negative-staining VLDL and mAB012 mixture. B: Representative VLDL particles bound with an antibody. C: Zoomed-in view of (B) showing the antibody details. D: A field of view of the same VLDL and mAB012 mixture except that this shows a frozen hydrated sample that used the cryo-EM plunge-freezing technique. E: Representative VLDL particles bound by an antibody. F: Zoomed-in view of (E) showing the antibody details. Scale bars, 50 nm.

Mentions: Through particle-by-particle 3D reconstructions, a few tens of VLDL-antibody complex particles were reconstructed. Six representative particles in increasing sizes are displayed at two directions that differ by 45° around the vertical axis (Fig. 3N). The resolutions of the final 3D reconstructions were ∼5.0 nm, which allowed us to model the particles’ surface shapes (Fig. 3O). The refined 3D density maps indicated obviously flat faces and the neighboring flat faces interacted to each other forming dihedral angles. The shapes can be modeled as polyhedrons by manually marking the vertices, connecting the vertices to represent the observed edges, and grouping the edges to represent the particle faces (Fig. 2N, O). The densities at the edges were generally higher than the densities on the surfaces (Fig. 2P, Q). In this model, only the dihedral angles larger than 20° were marked as edges, and therefore, a slight curvature of the faces was tolerated. By this method, there were more than 10 flat faces on each particle, in which a few dihedral angles were at or near 90°.


Polyhedral 3D structure of human plasma very low density lipoproteins by individual particle cryo-electron tomography 1 [S]
The 2D images of negative-staining and frozen VLDL complex with mAB012. A: Survey view of a negative-staining VLDL and mAB012 mixture. B: Representative VLDL particles bound with an antibody. C: Zoomed-in view of (B) showing the antibody details. D: A field of view of the same VLDL and mAB012 mixture except that this shows a frozen hydrated sample that used the cryo-EM plunge-freezing technique. E: Representative VLDL particles bound by an antibody. F: Zoomed-in view of (E) showing the antibody details. Scale bars, 50 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036368&req=5

f3: The 2D images of negative-staining and frozen VLDL complex with mAB012. A: Survey view of a negative-staining VLDL and mAB012 mixture. B: Representative VLDL particles bound with an antibody. C: Zoomed-in view of (B) showing the antibody details. D: A field of view of the same VLDL and mAB012 mixture except that this shows a frozen hydrated sample that used the cryo-EM plunge-freezing technique. E: Representative VLDL particles bound by an antibody. F: Zoomed-in view of (E) showing the antibody details. Scale bars, 50 nm.
Mentions: Through particle-by-particle 3D reconstructions, a few tens of VLDL-antibody complex particles were reconstructed. Six representative particles in increasing sizes are displayed at two directions that differ by 45° around the vertical axis (Fig. 3N). The resolutions of the final 3D reconstructions were ∼5.0 nm, which allowed us to model the particles’ surface shapes (Fig. 3O). The refined 3D density maps indicated obviously flat faces and the neighboring flat faces interacted to each other forming dihedral angles. The shapes can be modeled as polyhedrons by manually marking the vertices, connecting the vertices to represent the observed edges, and grouping the edges to represent the particle faces (Fig. 2N, O). The densities at the edges were generally higher than the densities on the surfaces (Fig. 2P, Q). In this model, only the dihedral angles larger than 20° were marked as edges, and therefore, a slight curvature of the faces was tolerated. By this method, there were more than 10 flat faces on each particle, in which a few dihedral angles were at or near 90°.

View Article: PubMed Central - PubMed

ABSTRACT

Human VLDLs assembled in the liver and secreted into the circulation supply energy to peripheral tissues. VLDL lipolysis yields atherogenic LDLs and VLDL remnants that strongly correlate with CVD. Although the composition of VLDL particles has been well-characterized, their 3D structure is elusive because of their variations in size, heterogeneity in composition, structural flexibility, and mobility in solution. Here, we employed cryo-electron microscopy and individual-particle electron tomography to study the 3D structure of individual VLDL particles (without averaging) at both below and above their lipid phase transition temperatures. The 3D reconstructions of VLDL and VLDL bound to antibodies revealed an unexpected polyhedral shape, in contrast to the generally accepted model of a spherical emulsion-like particle. The smaller curvature of surface lipids compared with HDL may also reduce surface hydrophobicity, resulting in lower binding affinity to the hydrophobic distal end of the N-terminal β-barrel domain of cholesteryl ester transfer protein (CETP) compared with HDL. The directional binding of CETP to HDL and VLDL may explain the function of CETP in transferring TGs and cholesteryl esters between these particles. This first visualization of the 3D structure of VLDL could improve our understanding of the role of VLDL in atherogenesis.

No MeSH data available.