Analysis of structure--function relationships in human apolipoprotein(a)

Area of Science:

• Biochemistry
• Cardiovascular Research
• Molecular Biology

Background:

• Elevated lipoprotein(a) (Lp(a)) is a significant risk factor for atherosclerosis.
• Lp(a) differs from low-density lipoprotein (LDL) due to the apolipoprotein(a) (apo(a)) component.
• The apo(a) structure contains kringle IV-like domains similar to plasminogen.

Purpose of the Study:

• To investigate the assembly mechanism of Lp(a) particles.
• To identify the specific molecular interactions involved in Lp(a) formation.
• To explore genetic variations in apo(a) and their functional implications.

Main Methods:

• Expression of recombinant apo(a) (r-apo(a)) with 17 kringle IV-like domains in human embryonic kidney cells.
• Site-directed mutagenesis to identify key residues in apo(a) mediating Lp(a) assembly.
• Polymerase chain reaction (PCR) amplification of liver apo(a) complementary DNA to study genetic polymorphisms.

Main Results:

• Demonstrated extracellular assembly of Lp(a) particles in plasma via covalent linkage of r-apo(a) to LDL.
• Identified a cysteine residue at position 4057 in apo(a) as the mediator of this covalent linkage.
• Discovered a polymorphism in apo(a) kringle IV type 10, leading to a threonine for methionine substitution, potentially enhancing Lp(a) interaction with lysine-Sepharose.

Conclusions:

• The study elucidates a key mechanism in Lp(a) particle assembly, involving a specific cysteine residue in apo(a).
• A genetic polymorphism in apo(a) may influence Lp(a) binding properties, potentially impacting its role in atherosclerosis.
• These findings contribute to understanding Lp(a) biology and may inform future therapeutic strategies for cardiovascular disease.