Lipid-protein interactions in human plasma LDL evidenced by magnetic resonance

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Low-density lipoprotein (LDL) particles possess a complex three-dimensional structure that remains incompletely understood at the molecular level.
• Investigating the interactions between the protein component (apolipoprotein B, apoB) and the lipid matrix is crucial for understanding LDL structure and function.

Purpose of the Study:

• To provide experimental evidence for direct non-covalent interactions between the protein part (apoB) and the lipid matrix of LDL particles.
• To elucidate the molecular-level interactions within LDL structure.

Main Methods:

• Utilized a combination of 1H Nuclear Magnetic Resonance (NMR) spectroscopy (600 MHz) and thiol-specific spin labeling of apoB.
• Analyzed spectral peak broadening in the 1H NMR spectra of LDL, specifically focusing on the methyl head groups of phosphatidylcholine and sphingomyelin.

Main Results:

• Line broadening of spectral peaks corresponding to phospholipid head groups was observed when apoB's free thiol groups were modified with a methanethiosulfonate spin label.
• This line broadening effect was comparable to that observed in the presence of a water-soluble paramagnetic compound, suggesting proximity.

Conclusions:

• The results indicate direct contact between specific fragments of apoB, particularly within the receptor binding region, and the solvated phospholipid head groups of the LDL lipid matrix.
• This provides experimental validation for the close association between apoB and the lipid components of LDL at a molecular level.