Structure of Human Apolipoprotein A-IV: A Distinct Domain Architecture among Exchangeable Apolipoproteins with Potential Functional Implications
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- 作者：Kevin Pearson ; Hiroyuki Saito ; Stephen C. Woods ; Sissel Lund-Katz ; Patrick Tso ; Michael C. Phillips ; and W. Sean Davidson
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：August 24, 2004
- 年：2004
- 卷：43
- 期：33
- 页码：10719 - 10729
- 全文大小：198K
- 年卷期：v.43,no.33(August 24, 2004)
- ISSN：1520-4995
文摘
Apolipoprotein A-IV (apoA-IV) is an exchangeable apolipoprotein that shares many functionalsimilarities with related apolipoproteins such as apoE and apoA-I but has also been implicated as acirculating satiety factor. However, despite the fact that it contains many predicted amphipathic 
-helicaldomains, relatively little is known about its tertiary structure. We hypothesized that apoA-IV exhibits acharacteristic functional domain organization that has been proposed to define apoE and apoA-I. To testthis, we created truncation mutants in a bacterial system that deleted amino acids from either the N- orC-terminal ends of human apoA-IV. We found that apoA-IV was less stable than apoA-I but was morehighly organized in terms of its cooperativity of unfolding. Deletion of the extreme N and C termini ofapoA-IV did not significantly affect the cooperativity of unfolding, but deletions past amino acid 333 onthe C terminus or amino acid 61 on the N terminus had major destabilizing effects. Functionally, apoA-IV was less efficient than apoA-I at clearing multilamellar phospholipid liposomes and promoting ATP-binding cassette transporter A1-mediated cholesterol efflux. However, deletion of a C-terminal region ofapoA-IV, which is devoid of predicted amphipathic helices (amino acids 333-376) stimulated both ofthese activities dramatically. We conclude that the amphipathic helices in apoA-IV form a single, largedomain that may be similar to the N-terminal helical bundle domains of apoA-I and apoE but that apoA-IV lacks the C-terminal lipid-binding and cholesterol efflux-promoting domain present in theseapolipoproteins. In fact, the C terminus of apoA-IV appears to reduce the ability of apoA-IV to interactwith lipids and promote cholesterol efflux. This indicates that, although apoA-IV may have evolved fromgene duplication events of ancestral apolipoproteins and shares the basic amphipathic helical buildingblocks, the overall localization of functional domains within the sequence is quite different from apoA-Iand apoE.
-helicaldomains, relatively little is known about its tertiary structure. We hypothesized that apoA-IV exhibits acharacteristic functional domain organization that has been proposed to define apoE and apoA-I. To testthis, we created truncation mutants in a bacterial system that deleted amino acids from either the N- orC-terminal ends of human apoA-IV. We found that apoA-IV was less stable than apoA-I but was morehighly organized in terms of its cooperativity of unfolding. Deletion of the extreme N and C termini ofapoA-IV did not significantly affect the cooperativity of unfolding, but deletions past amino acid 333 onthe C terminus or amino acid 61 on the N terminus had major destabilizing effects. Functionally, apoA-IV was less efficient than apoA-I at clearing multilamellar phospholipid liposomes and promoting ATP-binding cassette transporter A1-mediated cholesterol efflux. However, deletion of a C-terminal region ofapoA-IV, which is devoid of predicted amphipathic helices (amino acids 333-376) stimulated both ofthese activities dramatically. We conclude that the amphipathic helices in apoA-IV form a single, largedomain that may be similar to the N-terminal helical bundle domains of apoA-I and apoE but that apoA-IV lacks the C-terminal lipid-binding and cholesterol efflux-promoting domain present in theseapolipoproteins. In fact, the C terminus of apoA-IV appears to reduce the ability of apoA-IV to interactwith lipids and promote cholesterol efflux. This indicates that, although apoA-IV may have evolved fromgene duplication events of ancestral apolipoproteins and shares the basic amphipathic helical buildingblocks, the overall localization of functional domains within the sequence is quite different from apoA-Iand apoE.