A cross-linking study of apo-low density lipoprotein

Area of Science:

• Biochemistry
• Molecular Biology
• Lipid Metabolism

Background:

• Low-density lipoprotein (LDL) plays a crucial role in lipid transport.
• Apolipoprotein B (apo B) is the major protein component of LDL.
• Understanding apo B interactions is key to elucidating LDL structure and function.

Purpose of the Study:

• To investigate the interaction sites of apo B within human serum LDL.
• To determine if chemical cross-linking can identify intramolecular apo B interactions.
• To explore the accessibility of apo B interaction sites using dimethylsuberimidate.

Main Methods:

• Chemical cross-linking of LDL using dimethylsuberimidate.
• Analysis of apo B cross-linking patterns (intramolecular vs. intermolecular).
• Assessment of apo B molecular weight and potential dimerization.

Main Results:

• Extensive intermolecular cross-linking of apo B between different LDL particles was observed.
• Only a small fraction of intramolecularly cross-linked apo B dimer was formed within a single LDL.
• Dimethylsuberimidate primarily reacted with apo B on the surface of LDL particles.

Conclusions:

• The exposed or hydrophilic regions of LDL are distributed on its surface.
• The protein-protein interaction site of apo B is likely inaccessible to dimethylsuberimidate.
• This suggests the interaction site is shielded within the LDL structure, possibly beneath the surface layer.