Apolipoprotein A-I alpha -helices 7 and 8 modulate high density lipoprotein subclass distribution

Area of Science:

• Lipid metabolism
• Protein structure-function relationships
• Cardiovascular research

Background:

• Mice and humans exhibit distinct high-density lipoprotein (HDL) profiles.
• Human apolipoprotein A-I (apoA-I) transgenic mice display a human-like HDL profile.
• The amino acid sequence of apoA-I influences HDL subclass distribution.

Purpose of the Study:

• To investigate the role of specific alpha-helices in apoA-I in determining HDL subclass association.
• To identify the structural determinants of differential binding of apoA-I to HDL subclasses.

Main Methods:

• Expression of recombinant human, mouse, and chimeric apoA-I proteins in E. coli.
• Assessment of recombinant apoA-I binding to human plasma HDL subclasses (HDL(2) and HDL(3)).
• Evaluation of self-association, alpha-helicity, cholesterol efflux, and lecithin-cholesterol acyltransferase (LCAT) activity.

Main Results:

• Human apoA-I (T7-hAI) bound equally to HDL(2) and HDL(3).
• Mouse apoA-I (T7-mAI) preferentially bound to HDL(2).
• Chimeric apoA-I proteins confirmed that alpha-helices 7/8 dictate HDL subclass binding patterns.
• Differential self-association and LCAT activation by human and mouse apoA-I were independent of helices 7/8.

Conclusions:

• Alpha-helices 7 and 8 of apoA-I are critical determinants of HDL subclass distribution.
• Structural differences in apoA-I helices 7/8 account for species-specific HDL binding.
• Other regions of apoA-I contribute to differences in self-association and LCAT activity.