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

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• The apolipoprotein E (ApoE) family has three isoforms (ApoE4, E3, E2) crucial for lipoprotein metabolism and cholesterol transport.
• Apolipoprotein E4 (ApoE4) is a known risk factor for Alzheimer's disease, unlike ApoE3 and ApoE2.
• ApoE3 and ApoE4 differ by a single amino acid substitution: cysteine at position 112 in ApoE3 versus arginine in ApoE4.

Purpose of the Study:

• To investigate the structural differences between ApoE4 and ApoE3 using 19F NMR.
• To examine the influence of the C-terminal domain on the N-terminal domain's structure in ApoE isoforms.
• To elucidate the molecular basis for ApoE4's association with Alzheimer's disease risk.

Main Methods:

• Incorporation of 5-(19F)-tryptophan into ApoE proteins.
• Comparison of 1D 19F NMR spectra for N-terminal domains and full-length proteins.
• Analysis of wild-type ApoE3 and ApoE4 against C-terminal mutants under native and denaturing conditions.

Main Results:

• 19F NMR spectra of N-terminal domains were well-resolved, while full-length proteins showed conformational heterogeneity.
• Solvent exposure was observed for at least four tryptophan residues in wild-type proteins.
• Differences in tryptophan resonances within the N-terminal region indicate structural variations between ApoE3 and ApoE4, influenced by both the mutation and C-terminal interactions.

Conclusions:

• Structural distinctions between ApoE3 and ApoE4 exist within the N-terminal region.
• These structural differences arise from both the Arg158Cys mutation and interactions involving the C-terminal domain.
• The findings provide insights into the molecular mechanisms underlying ApoE4's role in Alzheimer's disease pathogenesis.