# ApoE isoform-specific structure: Insights on biology and pathobiology

> **NIH NIH U19** · MAYO CLINIC  JACKSONVILLE · 2021 · $565,375

## Abstract

PROJECT SUMMARY
A single amino acid difference in apolipoprotein E (apoE) distinguishes each of the three major
isoforms that lead to dramatically different functional outcomes when expressed in the brain:
apoE4 contributes up to a 15 fold risk increase in Alzheimer’s disease (AD) compared to apoE3,
whereas apoE2 appears to be protective. A large amount of evidence suggests a direct role of
the protein in disease progression; yet, the isoform- dependent structural features of apoE
remain elusive, hampering our understanding of the mechanism behind apoE4 neurotoxicity.
Indeed, current structural models of apoE have been derived from a limited number of
incomplete structures obtained from protein fragments free in solution or in complex with synthetic
liposomes. Very little is known about the structure in the context of endogenously-secreted
lipoproteins. Testing the ApoE Cascade Hypothesis (ACH), the core focus of this U19 proposal,
requires overcoming these limitations and comparing the structural differences of apoE isoforms
when bound to secreted lipoproteins and AD-related pathogenic molecules such as amyloid-β
(Aβ). Here, we propose to bypass previous experimental obstacles by using an innovative
multipronged approach that combines single- molecule fluorescence spectroscopy and cryo-
electron microscopy (EM). Our approach enables accessing the conformational ensemble of
apoE in its monomeric, oligomeric, and lipid-bound forms and reveals coexistence of multiple
conformations in equilibrium, which are invisible to classical methods of structural biology. In
collaboration with Core B, single-molecule measurements, negative-stain, and cryo-EM will be
compared and interpolated with molecular dynamics simulations to reconstruct atomistic-detailed
models of the protein when bound to secreted lipoproteins and Aβ. In Aim 1, we will determine
the isoform-specific structural ensemble of apoE/lipoprotein particles obtained from human apoE
knockin mouse-derived astrocytes, microglia, and vascular mural cells (Project 2 and 4), as well
as iPSC-derived cells (Core E), cell type-specific apoE mouse models (Projects 3-4), and human
biospecimens (Core C and D). In aim 2, we will assess how the interplay between Aβ
and apoE modulate their structural ensembles and oligomerization propensity. The
proposed experiments will provide a detailed atomistic structural representation of apoE
isoforms in the context of lipoproteins and while interacting with Aβ, integrating the biochemical
characterization of Core B, and facilitating investigations of isoform-specific functional effects
conducted by Projects 2-5 and Core B-F.

## Key facts

- **NIH application ID:** 10087385
- **Project number:** 1U19AG069701-01
- **Recipient organization:** MAYO CLINIC  JACKSONVILLE
- **Principal Investigator:** Andrea Soranno
- **Activity code:** U19 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $565,375
- **Award type:** 1
- **Project period:** 2021-06-01 → 2026-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10087385

## Citation

> US National Institutes of Health, RePORTER application 10087385, ApoE isoform-specific structure: Insights on biology and pathobiology (1U19AG069701-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10087385. Licensed CC0.

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