title: The roles of C-terminal helices of human apolipoprotein A-I in formation of high-density lipoprotein particles.
abstract: Apolipoprotein A-I (apoA-I) accepts cholesterol and phospholipids from ATP-binding cassette transporter A1 (ABCA1)-expressing cells to form high-density lipoprotein (HDL). Human apoA-I has two tertiary structural domains and the C-terminal domain (approximately amino acids 190-243) plays a key role in lipid binding. Although the high lipid affinity region of the C-terminal domain of apoA-I (residues 223-243) is essential for the HDL formation, the function of low lipid affinity region (residues 191-220) remains unclear. To evaluate the role of residues 191-220, we analyzed the structure, lipid binding properties, and HDL formation activity of Δ191-220 apoA-I, in comparison to wild-type and Δ223-243 apoA-I. Although deletion of residues 191-220 has a slight effect on the tertiary structure of apoA-I, the Δ191-220 variant showed intermediate behavior between wild-type and Δ223-243 regarding the formation of hydrophobic sites and lipid interaction through the C-terminal domain. Physicochemical analysis demonstrated that defective lipid binding of Δ191-220 apoA-I is due to the decreased ability to form α-helix structure which provides the energetic source for lipid binding. In addition, the ability to form HDL particles in vitro and induce cholesterol efflux from ABCA1-expressing cells of Δ191-220 apoA-I was also intermediate between wild-type and Δ223-243 apoA-I. These results suggest that despite possessing low lipid affinity, residues 191-220 play a role in enhancing the ability of apoA-I to bind to and solubilize lipids by forming α-helix upon lipid interaction. Our results demonstrate that the combination of low lipid affinity region and high lipid affinity region of apoA-I is required for efficient ABCA1-dependent HDL formation.
authors.affiliation: Institute of Health Biosciences, The University of Tokushima, 1-78-1 Shomachi, Tokushima 770-8505, Japan; Graduate School of Pharmaceutical Sciences, The University of Tokushima, 1-78-1 Shomachi, Tokushima 770-8505, Japan. Electronic address: nagao@tokushima-u.ac.jp.
authors.forename: Kohjiro
authors.initials: K
authors.lastname: Nagao
authors.forename: Mami
authors.initials: M
authors.lastname: Hata
authors.forename: Kento
authors.initials: K
authors.lastname: Tanaka
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takechi
authors.forename: David
authors.initials: D
authors.lastname: Nguyen
authors.forename: Padmaja
authors.initials: P
authors.lastname: Dhanasekaran
authors.forename: Sissel
authors.initials: S
authors.lastname: Lund-Katz
authors.forename: Michael C
authors.initials: MC
authors.lastname: Phillips
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Saito
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000502:physiology; D045744:Cell Line, Tumor; D002784:Cholesterol / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D006801:Humans; D008075:Lipoproteins, HDL / Q000235:genetics / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL; D002784:Cholesterol
keywords: 8-anilino-1-naphthalenesulfonic acid; ABC; ABCA1; ANS; ATP-binding cassette; ApoA-I; BHK; BSA; CD; Cholesterol; DMEM; DMPC; Dulbecco's modified Eagle's medium; FBS; GdnHCl; HDL; ITC; MLV; PBS; PC; SUV; UV; apo; apolipoprotein; baby hamster kidney; bovine serum albumin; circular dichroism; dimyristoyl phosphatidylcholine; fetal bovine serum; guanidine hydrochloride; high-density lipoprotein; isothermal titration calorimetry; multilamellar vesicle; phosphate-buffered saline; phosphatidylcholine; small unilamellar vesicle; ultraviolet