ABCA1 dimer-monomer interconversion during HDL generation revealed by single-molecule imaging.

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Medicine

Background:

• High-density lipoprotein (HDL) generation is crucial for preventing atherosclerosis.
• ATP-binding cassette protein A1 (ABCA1) mediates cholesterol and phospholipid transfer to apolipoprotein A-I (apoA-I) for HDL formation.
• Regulatory mechanisms of ABCA1 in HDL biogenesis are not fully understood.

Purpose of the Study:

• To investigate the role of ABCA1 dimerization in high-density lipoprotein (HDL) biogenesis.
• To elucidate the molecular mechanisms of ABCA1-mediated lipid transfer and HDL generation at the single-molecule level.

Main Methods:

• Single-molecule imaging using total internal reflection fluorescence microscopy (TIR-FM).
• Observation of ABCA1-green fluorescent protein (GFP) and apolipoprotein A-I (apoA-I) on the plasma membrane.
• Utilized an ATPase-deficient ABCA1 mutant to assess the role of ATPase activity in dimerization and function.

Main Results:

• Approximately 70% of ABCA1-GFP molecules on the plasma membrane were immobilized.
• Around 89% of immobile ABCA1 molecules existed as dimers.
• An ATPase-deficient ABCA1 mutant showed impaired immobilization and dimer formation.
• Apolipoprotein A-I (apoA-I) interaction with ABCA1 dimers is essential for discoidal HDL (dHDL) generation, followed by dimer-monomer interconversion.

Conclusions:

• ABCA1 dimerization is a critical prerequisite for apolipoprotein A-I (apoA-I) binding and nascent high-density lipoprotein (HDL) generation.
• The ABCA1 dimer functions as a receptor for two apoA-I molecules, facilitating dHDL particle formation.
• Understanding ABCA1 dimerization provides insights into atherosclerosis prevention and HDL biogenesis.