Probing the C-terminal domain of lipid-free apoA-I demonstrates the vital role of the H10B sequence repeat in HDL formation.
apoA-I plays important structural and functional roles in reverse cholesterol transport. We have described the molecular structure of the N-terminal domain, Δ(185-243) by X-ray crystallography. To understand the role of the C-terminal domain, constructs with sequential elongation of Δ(185-243), by increments of 11-residue sequence repeats were studied and compared with Δ(185-243) and WT apoA-I. Constructs up to residue 230 showed progressively decreased percent α-helix with similar numbers of helical residues, similar detergent and lipid binding affinity, and exposed hydrophobic surface. These observations suggest that the C-terminal domain is unstructured with the exception of the last 11-residue repeat (H10B). Similar monomer-dimer equilibrium suggests that the H10B region is responsible for nonspecific aggregation. Cholesterol efflux progressively increased with elongation up to ∼60% of full-length apoA-I in the absence of the H10B. In summary, the sequential repeats in the C-terminal domain are probably unstructured with the exception of H10B. This segment appears to be responsible for initiation of lipid binding and aggregation, as well as cholesterol efflux, and thus plays a vital role during HDL formation. Based on these observations and the Δ(185-243) crystal structure, we propose a lipid-free apoA-I structural model in solution and update the mechanism of HDL biogenesis.
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118.
Xiaohu
X
Mei
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118.
Minjing
M
Liu
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118.
Haya
H
Herscovitz
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118 Atkinson@bu.edu.
David
D
Atkinson
D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D002942:Circular Dichroism; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D005960:Glucosides / Q000737:chemistry; D057809:HEK293 Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008075:Lipoproteins, HDL / Q000096:biosynthesis*; D051379:Mice; D008958:Models, Molecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012996:Solutions
C505693:APOA1 protein, human; D016632:Apolipoprotein A-I; D005960:Glucosides; D008075:Lipoproteins, HDL; D012996:Solutions; C018619:octyl-beta-D-glucoside; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine
apolipoprotein A-I; cholesterol efflux; high density lipoprotein