The overall objective is to gain a more complete understanding of the structure of apolipoprotein (apo) E, especially as it relates to the ability of the protein to bind to heparin, the low density lipoprotein receptor (LDLR), and lipid particles of different size. Point mutations are known to give isoforms of apo E that function abnormally in cholesterol and triglyceride transport. A range of engineered apo E molecules expressed in E. coli is being used to address 3 specific aims. 1) To understand how interaction with phospholipid changes the conformation of apo E so that it can bind to the LDLR. The hypothesis being tested is that changes in alpha-helix organization alter the basic residue microenvironment in the LDLR binding domain (residues 136-150) which affects high affinity binding. NMR spectroscopy is used to monitor the microenvironments of lysine residues, and fluorescence and infrared spectroscopic methods are used to monitor the organization of apo E amphipathic alpha-helices in lipid-protein complexes. 2) To determine the type and organization of basic amino acids required in the apo E molecule for binding to heparin as opposed to the LDLR, and to understand why lipidation is required for binding of apo E to the LDLR but not for binding to heparin. The molecular mechanisms underlying changes in the energetics of binding arising from apo E polymorphism will also be investigated. 3) To understand the mechanisms responsible for the differing affinities of apo E isoforms for variously-sized serum lipoprotein particles, the molecular and thermodynamic parameters characterizing the binding of apo E and engineered variants to lipid particles of different sizes will be studied. The hypothesis being tested is that the length and properties (including the hydrophobicity of the nonpolar faces and the distribution of charged residues in the polar faces) of amphipathic alpha-helical segments in the C-terminal of the apo E molecule control lipid binding. Overall, achievement of these 3 aims will generate novel quantitative information about the ways in which apo E structure and polymorphism affect the functional properties of the protein in both physiological and pathological conditions. The design of ways to control the aberrant behavior of certain isoforms of apo E will be facilitated by this understanding.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL056083-08
Application #
6527075
Study Section
Special Emphasis Panel (ZRG1-SSS-T (01))
Program Officer
Applebaum-Bowden, Deborah
Project Start
1997-01-01
Project End
2005-07-31
Budget Start
2002-08-01
Budget End
2003-07-31
Support Year
8
Fiscal Year
2002
Total Cost
$340,000
Indirect Cost
Name
Children's Hospital of Philadelphia
Department
Type
DUNS #
073757627
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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Nguyen, David; Dhanasekaran, Padmaja; Nickel, Margaret et al. (2014) Influence of domain stability on the properties of human apolipoprotein E3 and E4 and mouse apolipoprotein E. Biochemistry 53:4025-33
Li, Hui; Dhanasekaran, Padmaja; Alexander, Eric T et al. (2013) Molecular mechanisms responsible for the differential effects of apoE3 and apoE4 on plasma lipoprotein-cholesterol levels. Arterioscler Thromb Vasc Biol 33:687-93
Kothapalli, Devashish; Castagnino, Paola; Rader, Daniel J et al. (2013) Apolipoprotein E-mediated cell cycle arrest linked to p27 and the Cox2-dependent repression of miR221/222. Atherosclerosis 227:65-71
Phillips, Michael C (2013) New insights into the determination of HDL structure by apolipoproteins: Thematic review series: high density lipoprotein structure, function, and metabolism. J Lipid Res 54:2034-48
Mizuguchi, Chiharu; Hata, Mami; Dhanasekaran, Padmaja et al. (2012) Fluorescence analysis of the lipid binding-induced conformational change of apolipoprotein E4. Biochemistry 51:5580-8
Kothapalli, Devashish; Liu, Shu-Lin; Bae, Yong Ho et al. (2012) Cardiovascular protection by ApoE and ApoE-HDL linked to suppression of ECM gene expression and arterial stiffening. Cell Rep 2:1259-71
Nguyen, David; Dhanasekaran, Padmaja; Nickel, Margaret et al. (2010) Molecular basis for the differences in lipid and lipoprotein binding properties of human apolipoproteins E3 and E4. Biochemistry 49:10881-9
Lund-Katz, Sissel; Phillips, Michael C (2010) High density lipoprotein structure-function and role in reverse cholesterol transport. Subcell Biochem 51:183-227
Koyama, Mao; Tanaka, Masafumi; Dhanasekaran, Padmaja et al. (2009) Interaction between the N- and C-terminal domains modulates the stability and lipid binding of apolipoprotein A-I. Biochemistry 48:2529-37

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