The carboxy-terminal region of apoA-I is required for the ABCA1-dependent formation of alpha-HDL but not prebeta-HDL particles in vivo.
ATP-binding cassette transporter A-1 (ABCA1)-mediated lipid efflux to lipid-poor apolipoprotein A-I (apoA-I) results in the gradual lipidation of apoA-I. This leads to the formation of discoidal high-density lipoproteins (HDL), which are subsequently converted to spherical HDL by the action of lecithin:cholesterol acyltransferase (LCAT). We have investigated the effect of point mutations and deletions in the carboxy-terminal region of apoA-I on the biogenesis of HDL using adenovirus-mediated gene transfer in apoA-I-deficient mice. It was found that the plasma HDL levels were greatly reduced in mice expressing the carboxy-terminal deletion mutants apoA-I[Delta(185-243)] and apoA-I[Delta(220-243)], shown previously to diminish the ABCA1-mediated lipid efflux. The HDL levels were normal in mice expressing the WT apoA-I, the apoA-I[Delta(232-243)] deletion mutant, or the apoA-I[E191A/H193A/K195A] point mutant, which promote normal ABCA1-mediated lipid efflux. Electron microscopy and two-dimensional gel electrophoresis showed that the apoA-I[Delta(185-243)] and apoA-I[Delta(220-243)] mutants formed mainly prebeta-HDL particles and few spherical particles enriched in apoE, while WT apoA-I, apoA-I[Delta(232-243)], and apoA-I[E191A/H193A/K195A] formed spherical alpha-HDL particles. The findings establish that (a) deletions that eliminate the 220-231 region of apoA-I prevent the synthesis of alpha-HDL but allow the synthesis of prebeta-HDL particles in vivo, (b) the amino-terminal segment 1-184 of apoA-I can promote synthesis of prebeta-HDL-type particles in an ABCA1-independent process, and (c) the charged residues in the 191-195 region of apoA-I do not influence the biogenesis of HDL.
Chroni
Angeliki
A
Institute of Biology, National Center for Scientific Research Demokritos, Agia Paraskevi, Athens 15310, Greece. achroni@bio.demokritos.gr
Koukos
Georgios
G
Duka
Adelina
A
Zannis
Vassilis I
VI
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000256:Adenoviridae / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D004591:Electrophoresis, Polyacrylamide Gel; D018014:Gene Transfer Techniques; D053442:High-Density Lipoproteins, Pre-beta / Q000096:biosynthesis*; D006801:Humans; D008055:Lipids; D008075:Lipoproteins, HDL / Q000096:biosynthesis*; D008099:Liver / Q000378:metabolism; D051379:Mice; D008854:Microscopy, Electron; D017434:Protein Structure, Tertiary / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D053442:High-Density Lipoproteins, Pre-beta; D008055:Lipids; D008075:Lipoproteins, HDL; D012333:RNA, Messenger