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Journal of Lipid Research, Vol. 50, 108-115, January 2009
Copyright © 2009 by American Society for Biochemistry and Molecular Biology

Structural and dynamic interfacial properties of the lipoprotein initiating domain of apolipoprotein B^*

Aubrey S. Ledford^*, Victoria A. Cook, Gregory S. Shelness^* and Richard B. Weinberg^1,,

^* Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, NC 27157
Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157
Department of Physiology & Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157

^* This work was supported by National Institutes of Health grants HL49373 (G.S.S.) and HL30897 (R.B.W.). A.S.L was supported by a predoctoral fellowship from the American Heart Association, Mid-Atlantic Affiliate.

Published, JLR Papers in Press, August 18, 2008.

¹ To whom correspondence should be addressed. e-mail: weinberg{at}wfubmc.edu

To better understand the earliest steps in the assembly of triglyceride (TG)-rich lipoproteins, we compared the biophysical and interfacial properties of two closely related apolipoprotein B (apoB) truncation mutants, one of which contains the complete lipoprotein initiating domain (apoB20.1; residues 1-912), and one of which, by virtue of a 50 amino acid C-terminal truncation, is incapable of forming nascent lipoproteins (apoB19; residues 1-862). Spectroscopic studies detected no major differences in secondary structure, and only minor differences in conformation and thermodynamic stability, between the two truncation mutants. Monolayer studies revealed that both apoB19 and apoB20.1 bound to and penetrated egg phosphatidylcholine (EPC) monolayers; however, the interfacial exclusion pressure of apoB20.1 was higher than apoB19 (25.1 mN/m vs. 22.8 mN/m). Oil drop tensiometry revealed that both proteins bound rapidly to the hydrophobic triolein/water interface, reducing interfacial tension by 20 mN/m. However, when triolein drops were first coated with phospholipids (PL), apoB20.1 bound with faster kinetics than apoB19 and also displayed greater interfacial elasticity (26.9 ± 0.8 mN/m vs. 22.9 ± 0.8 mN/m). These data establish that the transition of apoB to assembly competence is accompanied by increases in surface activity and elasticity, but not by significant changes in global structure.

Supplementary key words lipoprotein assembly • structure and function • fluorescence spectroscopy • circular dichroism spectroscopy • surface chemistry • monolayers • dynamic interfacial activity • very low density lipoproteins

Abbreviations: apoB, apolipoprotein B; CD, circular dichroism; EPC, egg phosphatidylcholine; ER, endoplasmic reticulum; GdnHCl, guanidine hydrochloride; LV, lipovitellin; MTP, microsomal triglyceride transfer protein; PBS, phosphate buffered saline; PL, phospholipid; TG, triglyceride

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