ApoE: In Vitro Studies of a Small Molecule Effector

Apolipoprotein E4 (apoE4), one of three isoforms of apoE, is the major risk factor for developing late onset Alzheimer's disease. The only differences among these isoforms (apoE2, apoE3, and apoE4) are single amino acid changes. Yet these proteins are functionally very different. One approach to ameliorating the effect of apoE4 with respect to Alzheimer's disease would be to find small molecular weight compounds that affect the behavior of apoE4. Few studies of this approach have been carried out in part because there was no complete structure of any full-length apoE isoform until 2011. Here, we focus on one small molecular weight compound, EZ-482, and explore the effects of its binding to apoE. Using hydrogen-deuterium exchange, we determined that EZ-482 binds to the C-terminal domains of both apoE3 and apoE4. The binding to apoE4, however, is accompanied by a unique N-terminal allosteric effect. Using fluorescence methods, we determined an apparent dissociation constant of approximately 8 μM. Although EZ-482 binds to the C-terminal domain, it blocks heparin binding to the N-terminal domain. The residues of apoE that bind heparin are the same as those involved in apoE binding to LDL and LRP-1 receptors. The methods and the data presented here may serve as a template for future studies using small molecular weight compounds to modulate the behavior of apoE.