Proteomic analysis of electronegative low-density lipoprotein

Area of Science:

• Biochemistry
• Proteomics
• Cardiovascular Research

Background:

• Low-density lipoprotein (LDL) is a complex particle with varying lipid and protein content.
• Apolipoprotein B (apoB) constitutes the majority of LDL protein, but minor proteins may influence its function.
• Electronegative LDL (LDL⁻) is an atherogenic subfraction distinct from native electropositive LDL (LDL(+)).

Purpose of the Study:

• To quantify and compare the content of minor proteins in LDL⁻ and LDL(+) subfractions.
• To identify specific apolipoproteins that differ between these LDL subfractions.
• To explore the potential impact of these protein differences on LDL characteristics.

Main Methods:

• Separation of LDL subfractions using anion exchange chromatography.
• Liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS) for protein identification.
• Confirmation of protein differences using immunoturbidimetry, ELISA, and Western blot.

Main Results:

• LC-ESI MS/MS identified up to 28 proteins in LDL fractions, with 13 common to all samples.
• LDL⁻ exhibited a significantly higher content of multiple minor proteins compared to LDL(+).
• Apolipoprotein F (apoF) and apolipoprotein J (apoJ) showed the most substantial increase (>15-fold) in LDL⁻.

Conclusions:

• The atherogenic LDL⁻ subfraction contains elevated levels of various apolipoproteins, notably apoF and apoJ.
• These protein compositional differences may contribute to the altered physicochemical properties of LDL⁻, including apoB misfolding and aggregation.
• Understanding these variations is crucial for elucidating LDL's role in atherogenesis.