TABLE 2.

Solution properties of apoA-II in lipid-free form and after lipidation

Condition	References
ApoA-II
Primary structure
Mature form: homodimer, 17.4 kDa, of two identical monomers, 77 amino acid residues linked by a single disulfide bond	(12, 36)
Secondary structure
33% α-helix; repeats of 11-mer amphipathic units	(15)
High surface activity	(17,18,19)
Tertiary structure
Low free energy of unfolding, 0.82 kcal/mol	(40)
Crystal structure: amphipathic helices aggregating into tetramers	(41)
Quaternary structure
Self-associates to a monomer-dimer-trimer equilibrium	(37, 38)
ApoA-II in discoidal particles
Increase in α-helical content from 33% to 69% upon interacting with phospholipids and cholesterol in aqueous suspensions	(45)
Total incorporation occurs at all initial lipid:protein ratios; lipid association preferred over self-association	(48)
Crystallographic and cross-linking studies of complexes hypothesize a belt-like orientation of apoA-II around a lipid bilayer	(41, 47)
ApoA-II in spherical particles, reconstitution studies
Sonication with HDL-derived lipids generates particles of a broad density and size distribution	(48)
Apo A-II containing spherical particles obtained by displacing apoA-I	(10, 98, 99)