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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.


Validation of the 3D reconstructions of cryo-ET VLDL-antibody complexes by a third party software, IMOD. The whole tomogram, which was low-pass filtered at 50 Å, is represented as an iso-surface view and is ramp-colored from red to blue by height. The whole tomogram contains approximately 100 VLDL particles with ∼80% bound to antibodies (mAB012). The high binding efficiency of the antibodies to VLDL in this equimolar ratio mixture indicates the high antibody specificity and confirms that these particles contain apoB protein. The VLDL-antibody complexes are each shaped like a garlic bulb, in which the antibody resembles an ∼10 nm-long stem, whereas the VLDL is shaped like a sphere with a 30 nm or larger diameter. Several ternary complexes exist, for which one antibody bridges two VLDL particles in each. Scale bars: 100 nm (A); 50 nm (B).
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f5: Validation of the 3D reconstructions of cryo-ET VLDL-antibody complexes by a third party software, IMOD. The whole tomogram, which was low-pass filtered at 50 Å, is represented as an iso-surface view and is ramp-colored from red to blue by height. The whole tomogram contains approximately 100 VLDL particles with ∼80% bound to antibodies (mAB012). The high binding efficiency of the antibodies to VLDL in this equimolar ratio mixture indicates the high antibody specificity and confirms that these particles contain apoB protein. The VLDL-antibody complexes are each shaped like a garlic bulb, in which the antibody resembles an ∼10 nm-long stem, whereas the VLDL is shaped like a sphere with a 30 nm or larger diameter. Several ternary complexes exist, for which one antibody bridges two VLDL particles in each. Scale bars: 100 nm (A); 50 nm (B).

Mentions: To validate our 3D reconstructions by a third-party method, we processed the same data for 3D reconstruction by IMOD (Fig. 5). The 3D reconstruction generated using IMOD (after low-pass filtering at 5.0 nm) showed that the VLDL-mAB012 complexes have a garlic bulb shape, in which the antibody resembled a ∼10 nm-long stem, whereas the VLDL was observed approximately as a sphere of 30 to ∼100 nm in diameter (Fig. 5). Among a total of ∼100 VLDL particles, ∼80% were bound with antibodies. The high binding efficiency of the antibody to VLDL in this equimolar ratio mixture indicates the high specificity of this antibody and confirms that these particles primarily contain apoB protein (Fig. 5). The results are consistent with our 3D reconstructions, suggesting that a bound antibody on a VLDL particle can be reconstructed by cryo-ET.


Polyhedral 3D structure of human plasma very low density lipoproteins by individual particle cryo-electron tomography 1 [S]
Validation of the 3D reconstructions of cryo-ET VLDL-antibody complexes by a third party software, IMOD. The whole tomogram, which was low-pass filtered at 50 Å, is represented as an iso-surface view and is ramp-colored from red to blue by height. The whole tomogram contains approximately 100 VLDL particles with ∼80% bound to antibodies (mAB012). The high binding efficiency of the antibodies to VLDL in this equimolar ratio mixture indicates the high antibody specificity and confirms that these particles contain apoB protein. The VLDL-antibody complexes are each shaped like a garlic bulb, in which the antibody resembles an ∼10 nm-long stem, whereas the VLDL is shaped like a sphere with a 30 nm or larger diameter. Several ternary complexes exist, for which one antibody bridges two VLDL particles in each. Scale bars: 100 nm (A); 50 nm (B).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Validation of the 3D reconstructions of cryo-ET VLDL-antibody complexes by a third party software, IMOD. The whole tomogram, which was low-pass filtered at 50 Å, is represented as an iso-surface view and is ramp-colored from red to blue by height. The whole tomogram contains approximately 100 VLDL particles with ∼80% bound to antibodies (mAB012). The high binding efficiency of the antibodies to VLDL in this equimolar ratio mixture indicates the high antibody specificity and confirms that these particles contain apoB protein. The VLDL-antibody complexes are each shaped like a garlic bulb, in which the antibody resembles an ∼10 nm-long stem, whereas the VLDL is shaped like a sphere with a 30 nm or larger diameter. Several ternary complexes exist, for which one antibody bridges two VLDL particles in each. Scale bars: 100 nm (A); 50 nm (B).
Mentions: To validate our 3D reconstructions by a third-party method, we processed the same data for 3D reconstruction by IMOD (Fig. 5). The 3D reconstruction generated using IMOD (after low-pass filtering at 5.0 nm) showed that the VLDL-mAB012 complexes have a garlic bulb shape, in which the antibody resembled a ∼10 nm-long stem, whereas the VLDL was observed approximately as a sphere of 30 to ∼100 nm in diameter (Fig. 5). Among a total of ∼100 VLDL particles, ∼80% were bound with antibodies. The high binding efficiency of the antibody to VLDL in this equimolar ratio mixture indicates the high specificity of this antibody and confirms that these particles primarily contain apoB protein (Fig. 5). The results are consistent with our 3D reconstructions, suggesting that a bound antibody on a VLDL particle can be reconstructed by cryo-ET.

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.