Polyhedral 3D structure of human plasma very low density lipoproteins by individual particle cryo-electron tomography1

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.

Three-dimensional structural dynamics of DNA origami Bennett linkages using individual-particle electron tomography

“…We used IPET and cryo-PS methods to reconstruct 3D maps of 129 individual DNA origami Bennett linkages. Although the resolution of obtained maps (no more than ~ 5 nm) was relatively low compared with the resolutions reported for rigid DNA origami 21 (~ 1 nm) and similar to our earlier reported ~ 5.0 nm resolution for very-low-density lipoprotein (using cryo-EM and IPET) 7 , these maps still provided enough information for us to obtain 129 conformations of Bennett linkage. The 129 conformations of Bennett linkages are the first observed dynamic DNA origami in 3D.…”

“…In the IPET iterative refinement process, automatically generated dynamic low-pass filters and soft masks were sequentially used. The IPET 3D reconstruction approach has been used to study the 3D structure and dynamics of DNA-nanogold conjugations 6 , very low density human lipoproteins 7 , immunoglobulin-G1 antibodies 8 , and many other macromolecules 9 – 12 .…”

Developing Electron Microscopy Tools for Profiling Plasma Lipoproteins Using Methyl Cellulose Embedment, Machine Learning and Immunodetection of Apolipoprotein B and Apolipoprotein(a)

“…As we previously observed with nanodiscs [ 36 ], thin films of mixed metal stain MC reduced the profile asymmetry so that the mean major–minor axes measurement ratio of adsorbed plasma LPs was 1.11 (SD = 0.096, n = 32), as compared to an expected ratio for LDL of 1.77 (major axis 21.4 ± 1.3 nm and minor axis 12.1 ± 1.1 nm [ 45 ]). This was consistent with the particles lying flat and presenting en face to the electron beam (note that this effect might not be relevant for larger, less asymmetric but angular VLDL particles [ 41 ]). Thus, our EM measurements tend to report maximal diameters, and so we applied a correction factor for the average diameter of an equivalent spheroid to facilitate comparison to results from other methodologies.…”

“…This produced striking contrast of heavily stained “blobs” of stain surrounding the LDL particles ( Figure 3 a–d). These “blobs” measured 13.37 nm, SD = 3.55, n = 70 (range 7–22 nm), which corresponded to published values for antibodies bound to LDL or very low-density lipoprotein (VLDL) [ 40 , 41 ]. The blobs were found only in presence of the primary antibody and increasing the concentration of antibody increased their number from approximately 1 to 3 per particle, labelling 100% of the particles ( Figure 3 e,f).…”

Oleic, palmitic triglycerides, very low density lipoproteins. Atherosclerosis, arterial atheromatosis and ischemic heart disease pathogenesis

“…Одновременно ω 9 лейкотриены, вместо синдрома компенсаторной противовоспали тельной защиты, стимулируют синдром системного воспалительного ответа, активи руя все проявления в организме биологиче ской реакции воспаления. Апогеем действия атеросклероза является формирование выра женной ГЛП, преимущественно типа IIв, и повышение в плазме крови содержания С реактивного белка [37].…”