The long-term objective of this project is to determine in molecular detain the energetic-structure-function relationship in exchangeable apolipoproteins, thereby providing an insight into molecular mechanisms of their action in the pathogenesis of atherosclerosis and other apolipoprotein-related disorders. Exchangeable apolipoproteins are water- soluble protein components of lipoproteins that mediate lipid and cholesterol transport and metabolism and play crucial roles in the pathogenesis of atherosclerosis, coronary heart disease, stroke, and other major human disorders including several forms of systemic and cerebral amyloidosis. Structural adaptability of apolipoproteins to heterogenous lipoprotein complexes and to plasma is absolutely essential for their functions, and has to be understood in detain in order to elucidate molecular mechanisms of apolipoprotein action in normal and in diseased states. The proposed work addresses this long-term goal through studies of the energetics, structure and folding pathway of the smallest human plasma apolipoprotein C-1 (apoC-1, 6 kDa). The ability of apoC-1 to activate lecitin: cholesterol acyltransferase (LCAT) may account for normal plasma levels of cholesterol esters in subjects with deficiency of the major LCAT activator, apoA-1. ApoC-1 delays the clearance of potentially atherogenic triglyceride-rich particles by inhibiting their uptake via the apoE-mediated low-density low-density lipoprotein receptor- related pathway. Thermodynamic and structural analyses of synthetic human apoC-1 and a series of its site-specific mutants targeted towards the predicted amphipathic alpha-helical regions will be carried out by using a combination of far-UV circular dichroism spectroscopy, differential scanning calorimetry, and x-ray diffraction methods. Such analysis will 1) dissect the folding pathway of lipid-free apoC-1 in solution, from partly folded monomeric to fully folded oligomeric or lipid-bound state; 2) determine, at the level of individual amino acids, the critical factors for the stability and cooperatively of the amphipathic alpha-helical structure in apoC-1; 3) determine the conformation apoC-1 in various self- associated status, such as 2D filaments and 3D crystals, to provide models fir a variety of functional apolipoprotein conformations. The results of this analysis will provide the energetic and structural basis for understanding mechanisms of functional apolipoprotein reactions and will help to understand their amyloidogenic properties, thereby leading to identification of rational therapeutic targets in a variety of apolipoprotein-related disorders.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
First Independent Research Support & Transition (FIRST) Awards (R29)
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Biophysical Chemistry Study Section (BBCB)
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Boston University
Schools of Medicine
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Gursky, Olga (2015) Structural stability and functional remodeling of high-density lipoproteins. FEBS Lett 589:2627-39
Das, Madhurima; Gursky, Olga (2015) Amyloid-Forming Properties of Human Apolipoproteins: Sequence Analyses and Structural Insights. Adv Exp Med Biol 855:175-211
Gao, Xuan; Yuan, Shujun; Jayaraman, Shobini et al. (2012) Role of apolipoprotein A-II in the structure and remodeling of human high-density lipoprotein (HDL): protein conformational ensemble on HDL. Biochemistry 51:4633-41
Jayaraman, Shobini; Jasuja, Ravi; Zakharov, Mikhail N et al. (2011) Pressure perturbation calorimetry of lipoproteins reveals an endothermic transition without detectable volume changes. Implications for adsorption of apolipoprotein to a phospholipid surface. Biochemistry 50:3919-27
Guha, Madhumita; Gursky, Olga (2010) Effects of oxidation on structural stability and remodeling of human very low density lipoprotein. Biochemistry 49:9584-93
Mehta, Ranjana; Gantz, Donald L; Gursky, Olga (2003) Human plasma high-density lipoproteins are stabilized by kinetic factors. J Mol Biol 328:183-92
Gursky, Olga; Ranjana; Gantz, Donald L (2002) Complex of human apolipoprotein C-1 with phospholipid: thermodynamic or kinetic stability? Biochemistry 41:7373-84
Gursky, O (2001) Solution conformation of human apolipoprotein C-1 inferred from proline mutagenesis: far- and near-UV CD study. Biochemistry 40:12178-85
Gursky, O; Aleshkov, S (2000) Temperature-dependent beta-sheet formation in beta-amyloid Abeta(1-40) peptide in water: uncoupling beta-structure folding from aggregation. Biochim Biophys Acta 1476:93-102
Gursky, O (1999) Probing the conformation of a human apolipoprotein C-1 by amino acid substitutions and trimethylamine-N-oxide. Protein Sci 8:2055-64