In situ delipidation-based structure of low-density lipoprotein and apolipoprotein B-100 physiologically imaged by...

Area of Science:

• Lipid Metabolism and Protein Structure
• Biophysics and Nanotechnology
• Biochemistry and Molecular Biology

Background:

• Apolipoprotein B-100 (apoB-100) is the primary structural protein in apoB-containing lipoproteins, such as low-density lipoprotein (LDL).
• The precise organization and lipidation process of apoB-100 within lipoprotein particles remain incompletely understood.
• Existing knowledge gaps hinder a full comprehension of lipoprotein structure-function relationships.

Purpose of the Study:

• To elucidate the in situ structural organization of apoB-100 during LDL delipidation.
• To visualize the dynamic changes in apoB-100 structure as lipids are removed under physiological conditions.
• To provide structural evidence for understanding apoB-100 lipidation and organization.

Main Methods:

• Utilized atomic force microscopy (AFM) combined with lipid depletion agents (Nonidet P-40 or methyl-β-cyclodextrin).
• Performed real-time, label-free imaging of LDL delipidation under physiological conditions.
• Analyzed concentration-dependent structural distributions of apoB-100 during the delipidation process.

Main Results:

• Successfully visualized sequential morphological changes of apoB-100 during LDL delipidation.
• Identified distinct structures including spheroidal, annular, C/U-shaped, and V/S/I-shaped forms.
• Correlated these structures with five proposed stages of LDL delipidation, from slightly delipidated to lipid-free apoB-100.

Conclusions:

• The study provides the first in situ visualization of LDL delipidation, revealing dynamic apoB-100 structural transitions.
• Findings offer structural evidence to resolve controversies regarding apoB-100 organization and lipidation.
• The AFM-based method presents a novel strategy for studying lipoprotein structure and has implications for designing lipid carriers.