Role of Helices and Loops in the Ability of Apolipophorin-III To Interact with Native Lipoproteins and Form Discoidal Lipoprotein Complexes
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- 作者：Palaniappan S. Chetty ; Estela L. Arrese ; Veronica Rodriguez ; and Jose L. Soulages
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：December 30, 2003
- 年：2003
- 卷：42
- 期：51
- 页码：15061 - 15067
- 全文大小：217K
- 年卷期：v.42,no.51(December 30, 2003)
- ISSN：1520-4995
文摘
The structure of Locusta migratoria apolipophorin-III consists of a five-helix bundle connectedby four short loops. The role of the conformational flexibility of helices and loops on the lipid-bindingactivity of this apolipoprotein was investigated by disulfide mediated tethering experiments. One disulfidemutant tethering the second and fourth loops (L2-L4), and two disulfide mutants restricting the flexibilityof the neighboring 
-helices 3 and 4 (H3-H4) and 1 and 5 (H1-H5), were studied. The ability of thedisulfide mutants to interact with phospholipid vesicles, mixed micelles of phosphatidylcholine and cholate,and in vivo with native spherical lipoprotein particles was studied. The L2-L4 mutant was active withnative lipoproteins as well as being able to form discoidal lipoproteins upon incubation with either liposomesor discoidal micelles. The H3-H4 mutant was not able to interact with liposomes or native lipoproteinsbut interacted with discoidal micelles. The H1-H5 mutant was unable to interact with lipid in any of thethree systems. Three conclusions were reached: (1) opening of the helix bundle does not require theseparation of loops 2 and 4 as recently proposed by others and (2) -helices 3 and/or 4 are involved inthe insertion of apoLp-III in both phospholipid bilayers and monolayers. The conformational flexibilityof helices 3 and 4 is required for the lipid-binding activity of apoLp-III. (3) Interaction of helices 1 and/or5 with the lipid surface is required to the formation of stable lipoprotein complexes of any kind.
-helices 3 and 4 (H3-H4) and 1 and 5 (H1-H5), were studied. The ability of thedisulfide mutants to interact with phospholipid vesicles, mixed micelles of phosphatidylcholine and cholate,and in vivo with native spherical lipoprotein particles was studied. The L2-L4 mutant was active withnative lipoproteins as well as being able to form discoidal lipoproteins upon incubation with either liposomesor discoidal micelles. The H3-H4 mutant was not able to interact with liposomes or native lipoproteinsbut interacted with discoidal micelles. The H1-H5 mutant was unable to interact with lipid in any of thethree systems. Three conclusions were reached: (1) opening of the helix bundle does not require theseparation of loops 2 and 4 as recently proposed by others and (2) -helices 3 and/or 4 are involved inthe insertion of apoLp-III in both phospholipid bilayers and monolayers. The conformational flexibilityof helices 3 and 4 is required for the lipid-binding activity of apoLp-III. (3) Interaction of helices 1 and/or5 with the lipid surface is required to the formation of stable lipoprotein complexes of any kind.