Behavior of human apolipoprotein E in aqueous solutions and at interfaces

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Human plasma apolipoprotein E (apo-E) is crucial for lipid metabolism.
• Understanding apo-E's self-association and lipid-binding properties is key to its function.

Purpose of the Study:

• To investigate the self-association behavior of human plasma apo-E in aqueous solution.
• To characterize the interaction of apo-E with lipid surfaces and particles.
• To elucidate the structural basis for apo-E's functional properties.

Main Methods:

• Aqueous solution studies at physiological pH and ionic strength.
• Surface pressure measurements at the air-water interface.
• Binding studies with phosphatidylcholine-coated triolein particles.

Main Results:

• Apo-E forms stable tetramers in solution, predominantly in an alpha-helical conformation.
• Tetramerized apo-E exhibits stable monolayer formation at the air-water interface with specific collapse pressure and molecular area.
• Reversible binding to lipid particles was observed, with a dissociation constant and binding saturation level comparable to other apolipoproteins.
• Alpha-helix content increases upon transfer to the lipid surface.

Conclusions:

• The amphiphilic alpha-helical structure of apo-E is fundamental to its self-association and lipid-binding capabilities.
• Apo-E can readily dissociate from lipoprotein surfaces to form soluble tetramers.
• These findings provide insights into apo-E's role in lipoprotein assembly and lipid transport.