Structural differences between apolipoprotein E3 and E4 as measured by (19)F NMR

Protein Sci. 2010 Jan;19(1):66-74. doi: 10.1002/pro.283.

Abstract

The apolipoprotein E family contains three major isoforms (ApoE4, E3, and E2) that are directly involved with lipoprotein metabolism and cholesterol transport. ApoE3 and apoE4 differ in only a single amino acid with an arginine in apoE4 changed to a cysteine at position 112 in apoE3. Yet only apoE4 is recognized as a risk factor for Alzheimer's disease. Here we used (19)F NMR to examine structural differences between apoE4 and apoE3 and the effect of the C-terminal domain on the N-terminal domain. After incorporation of 5-(19)F-tryptophan the 1D (19)F NMR spectra were compared for the N-terminal domain and for the full length proteins. The NMR spectra of the N-terminal region (residues 1-191) are reasonably well resolved while those of the full length wild-type proteins are broad and ill-defined suggesting considerable conformational heterogeneity. At least four of the seven tryptophan residues in the wild type protein appear to be solvent exposed. NMR spectra of the wild-type proteins were compared to apoE containing four mutations in the C-terminal region that gives rise to a monomeric form either of apoE3 under native conditions (Zhang et al., Biochemistry 2007; 46: 10722-10732) or apoE4 in the presence of 1 M urea. For either wild-type or mutant proteins the differences in tryptophan resonances in the N-terminal region of the protein suggest structural differences between apoE3 and apoE4. We conclude that these differences occur both as a consequence of the Arg158Cys mutation and as a consequence of the interaction with the C-terminal domain.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Apolipoprotein E3 / chemistry*
  • Apolipoprotein E3 / genetics
  • Apolipoprotein E3 / metabolism
  • Apolipoprotein E4 / chemistry*
  • Apolipoprotein E4 / genetics
  • Apolipoprotein E4 / metabolism
  • Fluorine / chemistry
  • Models, Molecular
  • Mutation
  • Nuclear Magnetic Resonance, Biomolecular / methods*
  • Protein Denaturation
  • Protein Structure, Tertiary
  • Urea / chemistry

Substances

  • Apolipoprotein E3
  • Apolipoprotein E4
  • Fluorine
  • Urea