Understanding the Inhibition of the Alzheimer's Ab peptide by Human Serum Albumin

Abstract

<p>Aggregation of the<strong> </strong>Alzheimer’s Aβ peptide in the brain and blood plasma is controlled by endogenous Aβ binding proteins. The structural basis for the interaction between the Aβ peptide and the Aβ binding proteins is critical not only to understand how Aβ amyloids are controlled in vivo, but also to guide the design of novel Aβ-self association inhibitors. However, the current knowledge of the structures of the Aβ/Aβ binding protein complexes is still sparse. This thesis focuses mainly on the interaction of the Aβ peptide with Human Serum Albumin (HSA). It is known that HSA binds ~90% of the Aβ in human plasma and prevents the Aβ self-association into amyloid fibrils. However, the mechanism of Aβ self-association inhibition by albumin was not understood prior to our work. We have shown that albumin preferentially binds toxic Aβ oligomers and fibrils inhibiting their growth into larger Aβ assemblies through a “monomer competitor” mechanism. Using a combination of NMR, domain deletion mutants, dynamic light scattering and ultrafiltration we have investigated the stoichiomery and affinity of the Aβ oligomer: HSA complexes. Our results indicate that all three domains of HSA bind Aβ oligomers and fibrils with an affinity in the 1-100 nM range. Such binding site degeneracy explains how albumin minimizes competition by other ligands such as fatty acids and drugs. Moreover we have used the soluble and NMR suitable domain 3 of albumin to dissect further the determinants of the Aβ oligomer binding to albumin at subdomain and peptide resolution. We show that both subdomains of the HSA domain 3 (<em>i.e</em>. 3A and 3B) bind the Aβ oligomers. In addition, we identified a peptide sequence within subdomain 3B that displays significant potency in the inhibition of Aβ self-association.</p>