Eric Arehart

Date of Award

8-2003

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Biochemistry

Advisor

Howard Patterson

Second Committee Member

Rebecca van Beneden

Third Committee Member

Robert E. Cashon

Abstract

Low-density lipoproteins (LDL) and very low-density lipoproteins (VLDL) are essential for transporting cholesterol and triglycerides in the blood. Intimate to this process is the interaction between the lipoprotein molecule and its cellular receptor. This pathway involves the LDL receptor (LDLR) interacting with apolipoprotein Apo B-100 in both LDLs and VLDLs and additionally lipoprotein lipase (LPL) with Apo C-I1 in the case of VLDL. Recent investigations link 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure in humans to heart disease. Due to TCDD's non-polar nature, it is reasonable to expect this compound to bind serum lipoproteins in vivo. Here we show TCDD to tightly bind human LDL and VLDL in vitro inducing a change in the lipoprotein conformation using fluorescence spectroscopy. We also show TCDD's ability to bind Trp-48 within the lipase binding region of apolipoprotein C-11. In order to understand TCDD's affinity for the protein components of lipoproteins, computational studies show TCDD's ability to form hydrogen bonds with certain amino acid residues, specifically tryptophan. These results indicate TCDD has a far greater ability to bind protein components within lipoprotein molecules compared with polychlorinated biphenyls (PCBs) controls. Circular dichroism spectroscopy (CD) shows that TCDD binding LDL and apolipoprotein C-I1 denatures the protein's secondary structure. In the case of apolipoprotein C-11, the inner core composed of a four-a-helix bundle is lost. CD also shows denaturing of LDL when treated with TCDD with a loss of both a-helix and Psheet secondary structure. These studies show that at low concentrations of TCDD (3: 1 TCDD to protein), TCDD binds and diminishes overall protein structure. Furthermore, this work shows that when TCDD binds the apolipoprotein C-11, apoC-I1 is unable to bind lipoprotein lipase. This interaction may lead to the inactivation of LDL and VLDL receptor recognition contributing to a buildup of serum lipoproteins and lipids thus hastening the development of atherosclerosis.

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