VLDL lipolysis products increase VLDL fluidity and convert apolipoprotein E4 into a more expanded conformation

Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India.
The Journal of Lipid Research (Impact Factor: 4.73). 12/2009; 51(6):1273-83. DOI: 10.1194/jlr.M000406
Source: PubMed

ABSTRACT Our previous work indicated that apolipoprotein (apo) E4 assumes a more expanded conformation in the postprandial period. The postprandial state is characterized by increased VLDL lipolysis. In this article, we tested the hypothesis that VLDL lipolysis products increase VLDL particle fluidity, which mediates expansion of apoE4 on the VLDL particle. Plasma from healthy subjects was collected before and after a moderately high-fat meal and incubated with nitroxyl-spin labeled apoE. ApoE conformation was examined by electron paramagnetic resonance spectroscopy using targeted spin probes on cysteines introduced in the N-terminal (S76C) and C-terminal (A241C) domains. Further, we synthesized a novel nitroxyl spin-labeled cholesterol analog, which gave insight into lipoprotein particle fluidity. Our data revealed that the order of lipoprotein fluidity was HDL approximately LDL<VLDL<VLDL+lipoprotein lipase. Moreover, the conformation of apoE4 depended on the lipoprotein fraction: VLDL-associated apoE4 had a more linear conformation than apoE4 associated with LDL or HDL. Further, by changing VLDL fluidity, VLDL lipolysis products significantly altered apoE4 into a more expanded conformation. Our studies indicate that after every meal, VLDL fluidity is increased causing apoE4 associated with VLDL to assume a more expanded conformation, potentially enhancing the pathogenicity of apoE4 in vascular tissue.


Available from: Madhu S Budamagunta, Sep 15, 2014
1 Follower
  • [Show abstract] [Hide abstract]
    ABSTRACT: Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism and responsible for catalyzing lipolysis of triglycerides in lipoproteins. LPL is produced mainly in adipose tissue, skeletal and heart muscle, as well as in macrophage and other tissues. After synthesized, it is secreted and translocated to the vascular lumen. LPL expression and activity are regulated by a variety of factors, such as transcription factors, interactive proteins and nutritional state through complicated mechanisms. LPL with different distributions may exert distinct functions and have diverse roles in human health and disease with close association with atherosclerosis. It may pose a pro-atherogenic or an anti-atherogenic effect depending on its locations. In this review, we will discuss its gene, protein, synthesis, transportation and biological functions, and then focus on its regulation and relationship with atherosclerosis and potential underlying mechanisms. The goal of this review is to provide basic information and novel insight for further studies and therapeutic targets. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.
    Atherosclerosis 10/2014; 237(2):597-608. DOI:10.1016/j.atherosclerosis.2014.10.016 · 3.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We found earlier that apolipoprotein A-I (apoA-I) variants that induced hypertriglyceridemia (HTG) in mice had increased affinity to triglyceride (TG)-rich lipoproteins and thereby impaired their catabolism. Here, we tested if a naturally occurring human apoA-I mutation, Lys107del, associated with HTG also promotes apoA-I binding to TG-rich particles. We expressed apoA-I[Lys107del] variant in E.coli, studied its binding to TG-rich emulsion particles, and performed a physicochemical characterization of the protein. Compared to WT apoA-I, apoA-I[Lys107del] showed enhanced binding to TG-rich particles, lower stability, and greater exposure of hydrophobic surfaces. The crystal structure of truncated, Δ(185-243), apoA-I (Mei and Atkinson, 2011) suggests that deletion of Lys107 disrupts helix registration and disturbs a stabilizing salt-bridge network in the N-terminal helical bundle. To elucidate the structural changes responsible for the altered function of apoA-I[Lys107del], we studied another mutant, apoA-I[Lys107Ala]. Our findings suggest that the registry shift and ensuing disruption of the inter-helical salt bridges in apoA-I[Lys107del] result in destabilization of the helical bundle structure and greater exposure of hydrophobic surfaces. We conclude that the structural changes in the apoA-I[Lys107del] variant facilitate its binding to TG-rich lipoproteins and thus, may reduce their lipolysis and contribute to the development of HTG in carriers of the mutation.
    The Journal of Lipid Research 06/2014; 55(9). DOI:10.1194/jlr.M047241 · 4.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the interaction between Dipalmitoylphosphatidylcholine (DPPC) and a nitroxide spin label in order to understand its influences on lipid structure and dynamics using molecular dynamics simulations. The system was modified by covalentlyattaching nitroxide spin labels to the headgroups of two DPPC molecules. (S-(2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)methyl methanesulfonothioate) (MTSL) was used as the spin label. The label position and dynamics were analyzed as was the impactof the modified DPPC on the structure of the surrounding lipids. The modified DPPC molecules locate closer to the center of the membrane than unmodified DPPC molecules. The rotation of the spin label is unrestricted, but there are favored orientations. MTSL depresses the deuterium order parameters of the carbon atoms close to the headgroup in surrounding DPPC molecules. The spin label has no impact on order parameters of carbon atoms at the end of the lipid tails. The lateral diffusion constant of the modified DPPC is indistinguishable from unmodified DPPC molecules. These novel computational results suggest an experimental validation.
    Biochimica et Biophysica Acta 08/2013; 1828(11). DOI:10.1016/j.bbamem.2013.07.030 · 4.66 Impact Factor