NATIVE COMPLEX-FORMATION BETWEEN APOLIPOPROTEIN-E ISOFORMS AND THE ALZHEIMERS-DISEASE PEPTIDE A-BETA

TO explore whether the genetic linkage between apolipoprotein E (ApoE) alleles and susceptibility to Alzheimer's disease might be attributab le to a direct molecular interaction between ApoE and the amyloid pept ide A beta, we have produced ApoE variants in Escherichia coli and stu died their interactions with A beta under native conditions. When incu bated with A beta at 20-40 mu M concentrations, all three isoforms of ApoE (2, 3, and 4) readily form complexes with A beta which can be iso lated by gel filtration in native buffer. Freshly mixed ApoE and A bet a generate a complex that co-migrates in gel filtration with the main A(280) peak, which migrates identically to the ApoE tetramer alone. Af ter several hours incubation, an additional, high molecular weight, so luble aggregate appears which also contains both ApoE and A beta. Neit her ApoE nor A beta incubated by themselves produces high molecular we ight aggregates under these conditions, Incubation of A beta with cont rol proteins bovine serum albumin and immunoglobulin generates negliga ble binding in the gel filtration assay. Similar results were obtained whether A beta(1-40) or A beta(1-42) was used, and plasma-derived Apo E gave similar results to E. coli-produced material. The data are cons istent with a role for ApoE-A beta interactions in modulating the deve lopment of AD. Since no major differences were observed in the behavio r of the three ApoE isotypes, however, the molecular basis of the gene tic trend between ApoE alleles and AD cannot be attributed to specific activity differences between the molecular forms of ApoE characterize d in this study.