125I-labeled ApoE binds competitively to β(1-40) fibrils with pathological chaperone proteins

Abstract

Radiolabeled Apolipoprotein E (Apo E) was used in a competitive binding filtration assay to amyloid fibrils preformed from β(1-40) peptide as a probe of the binding sites for proteins either found in senile plaques in Alzheimer's Disease brain or reported to be associated with the soluble peptide. Apo E, Apo J, Apo A-I, Apo B, laminin, complement components C3 and C4, and al-antichymotrypsin all displayed sub-micromolar apparent affinities for the Apo E binding site on fibrils. Transthyretin, α2-macroglobulin, amyloid P protein, heparan sulfate proteoglycan, complement component Clq, chondroitin sulfate A, and GM1 gan-glioside were much less effective. The ϵ2, ϵ3, and ϵ4 isoforms of Apo E showed different affinities for fibrils and lipidation of these lipoproteins made little difference. Other fibrillar β-peptides also bound Apo E, with Aβ40 ∼ Aβ42 > Aβ(12-28); Aβ(25-35) = 0.A series of soluble β-peptides and fragments failed to effect Apo E binding. Thus, both conformational and quaternary structural features are important in high affinity binding of Apo E to Aβ40 fibrils. Different amyloid plaque-associated molecules apparently associate with alternative primary and secondary structural features on fibrils.