Abstract
Interaction of the amino- and carboxyl-terminal domains in apolipoprotein (apo) E, referred to as domain interaction, is predicted to be more pronounced in apoE4 than in apoE3 and to underlie the association of apoE4 with Alzheimer and cardiovascular diseases. However, direct physical proof for the domain interaction concept is lacking. To address this issue, fluorescence resonance energy transfer and electron paramagnetic resonance spectroscopy were used to probe the spatial proximity of the two domains of apoE. Both methods demonstrated that the two domains are closer in both lipid-free and phospholipid-bound apoE4 than in apoE3 as a result of domain interaction. In addition, as shown by electron paramagnetic resonance, the domains of apoE4 move apart to resemble more closely the distance in apoE3 when the isoforms are bound to triglyceride-rich emulsion particles. These results demonstrate that domain interaction is a structural property of apoE4 and that apoE adopts different conformations when complexed to different lipids.
Highlights
Interaction of the amino- and carboxyl-terminal domains in apolipoprotein E, referred to as domain interaction, is predicted to be more pronounced in apoE4 than in apoE3 and to underlie the association of apoE4 with Alzheimer and cardiovascular diseases
The importance of Arg-61 and Glu-255 for domain interaction was demonstrated by site-directed mutagenesis in which replacement of either Arg-61 with threonine or Glu-255 with alanine alters the binding preference of apoE4 from very low density lipoprotein to high density lipoprotein [13]
Two variants of the fluorescence resonance energy transfer (FRET) construct, FC1 and FC2, were prepared to assess the influence of domain interaction on the conformation
Summary
Direct physical proof for the domain interaction concept is lacking To address this issue, fluorescence resonance energy transfer and electron paramagnetic resonance spectroscopy were used to probe the spatial proximity of the two domains of apoE. As shown by electron paramagnetic resonance, the domains of apoE4 move apart to resemble more closely the distance in apoE3 when the isoforms are bound to triglyceride-rich emulsion particles These results demonstrate that domain interaction is a structural property of apoE4 and that apoE adopts different conformations when complexed to different lipids. These sequence differences dictate different structural and biophysical properties that result in functional differences that are predicted to affect disease One such property is the concept of domain interaction, originally proposed based on the differential binding of apoE4 to large triglyceride-rich very low density lipoproteins and apoE3 to smaller high density lipoproteins associated. Based on the EPR data, a model of the spatial proximity of the amino- and carboxylterminal domains is proposed
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