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Apolipoprotein A-I Self-Association and the Formation of High Density Lipoprotein

Topbas, Celalettin

Abstract Details

2015, Doctor of Philosophy in Clinical-Bioanalytical Chemistry, Cleveland State University, College of Sciences and Health Professions.
It is generally accepted that apolipoprotein A-I (apoA-I), the main protein constituent of high density lipoprotein (HDL), forms a dimeric antiparallel structure that confers nascent HDL function and stability and provides a scaffold for the lipid phase. Moreover, while the truncated lipid-free apoA-I crystal structures suggest more compact helical bundle structure, the solution structure of full length lipid-free apoA-I is unclear, and the mechanism of how monomeric lipid-free apoA-I associates in antiparallel fashion during HDL formation is shrouded in mystery. Here in this study we performed hydrogen-deuterium exchange (HDX) and lipidation kinetic analyses of monomeric and multimeric (predominantly dimeric) apoA-I employing both mass spectrometry (HDX-MS) and functional lipidation assays. At lower concentration (0.07 mg/ml) lipid-free apoA-I is monomeric (based on equilibrium PAGE and cross-linking studies) and exhibits multiple discrete yet reproducible regions with bimodal HDX kinetics indicative of the existence of distinct populations of molecules that have domains with alternative secondary structure (random coil vs. helical). Kinetic HDX studies further reveal that at higher concentration (0.7 mg/ml) lipid-free apoA-I self-association promotes a conformational change of the C-terminus domain E223-A232 from random coil to alpha-helix. Surprisingly, apoA-I self-association seems to bury E223-A232 within the binding interface, which significantly slows down the rate of apoA-I lipidation. Peptide competition assays show that N- and C-terminus peptides (K12-D24 and E223-A232, respectively) interfere with apoA-I self-association, but only the C-terminus peptide blocks apoA-I lipidation. Taken together, the findings of this thesis indicate that HDL genesis starts with lipidation of apoA-I monomers followed by apoA-I dimerization in an antiparallel fashion on the lipid surface.
Valentin Gogonea, PhD (Committee Chair)
Stanley Hazen, MD. PhD (Committee Member)
Jonathan Smith, PhD (Committee Member)
David Anderson, PhD (Committee Member)
Joseph Didonato, PhD (Committee Member)
Mekki Bayachou, PhD (Committee Member)
110 p.

Recommended Citations

Citations

  • Topbas, C. (2015). Apolipoprotein A-I Self-Association and the Formation of High Density Lipoprotein [Doctoral dissertation, Cleveland State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=csu1440347923

    APA Style (7th edition)

  • Topbas, Celalettin. Apolipoprotein A-I Self-Association and the Formation of High Density Lipoprotein. 2015. Cleveland State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=csu1440347923.

    MLA Style (8th edition)

  • Topbas, Celalettin. "Apolipoprotein A-I Self-Association and the Formation of High Density Lipoprotein." Doctoral dissertation, Cleveland State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1440347923

    Chicago Manual of Style (17th edition)