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https://hdl.handle.net/2440/66118
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Type: | Journal article |
Title: | Aromatic residues in the C-terminal helix of human apoC-I mediate phospholipid interactions and particle morphology |
Author: | James, P. Dogovski, C. Dobson, R. Bailey, M. Goldie, K. Karas, J. Scanlon, D. O'Hair, R. Perugini, M. |
Citation: | Journal of Lipid Research, 2009; 50(7):1384-1394 |
Publisher: | Amer Soc Biochemistry Molecular Biology Inc |
Issue Date: | 2009 |
ISSN: | 0022-2275 1539-7262 |
Statement of Responsibility: | Patrick F. James, Con Dogovski, Renwick C. J. Dobson, Michael F. Bailey, Kenneth N. Goldie, John A. Karas, Denis B. Scanlon, Richard A. J. OʼHair, and Matthew A. Perugini |
Abstract: | Human apolipoprotein C-I (apoC-I) is an exchangeable apolipoprotein that binds to lipoprotein particles in vivo. In this study, we employed a LC-MS/MS assay to demonstrate that residues 38–51 of apoC-I are significantly protected from proteolysis in the presence of 1,2-dimyristoyl-3-sn-glycero-phosphocholine (DMPC). This suggests that the key lipid-binding determinants of apoC-I are located in the C-terminal region, which includes F42 and F46. To test this, we generated site-directed mutants substituting F42 and F46 for glycine or alanine. In contrast to wild-type apoC-I (WT), which binds DMPC vesicles with an apparent Kd [Kd(app)] of 0.89 μM, apoC-I(F42A) and apoC-I(F46A) possess 2-fold weaker affinities for DMPC with Kd(app) of 1.52 μM and 1.58 μM, respectively. However, apoC-I(F46G), apoC-I(F42A/F46A), apoC-I(F42G), and apoC-I(F42G/F46G) bind significantly weaker to DMPC with Kd(app) of 2.24 μM, 3.07 μM, 4.24 μM, and 10.1 μM, respectively. Sedimentation velocity studies subsequently show that the protein/DMPC complexes formed by these apoC-I mutants sediment at 6.5S, 6.7S, 6.5S, and 8.0S, respectively. This is compared with 5.0S for WT apoC-I, suggesting the shape of the particles was different. Transmission electron microscopy confirmed this assertion, demonstrating that WT forms discoidal complexes with a length-to-width ratio of 2.57, compared with 1.92, 2.01, 2.16, and 1.75 for apoC-I(F42G), apoC-I(F46G), apoC-I(F42A/F46A), and apoC-I(F42G/F46G), respectively. Our study demonstrates that the C-terminal amphipathic α-helix of human apoC-I contains the major lipid-binding determinants, including important aromatic residues F42 and F46, which we show play a critical role in stabilizing the structure of apoC-I, mediating phospholipid interactions, and promoting discoidal particle morphology. |
Keywords: | analytical ultracentrifugation apo C1 CI electron microscopy lipid metabolism lipidomics mass spectrometry phospholipid protein-lipid interaction |
Rights: | Copyright ©2009 by the American Society for Biochemistry and Molecular Biology, Inc. |
DOI: | 10.1194/jlr.M800529-JLR200 |
Published version: | http://dx.doi.org/10.1194/jlr.m800529-jlr200 |
Appears in Collections: | Aurora harvest Chemistry publications |
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