A structural motif of acetylcholinesterase that promotes amyloid beta-peptide fibril formation

Acetylcholinesterase (AChE) has been found to be associated with the core o f senile plaques. We have shown that AChE interacts with the amyloid beta - peptide (A beta) and promotes amyloid fibril formation by a hydrophobic env ironment close to the peripheral anionic binding site (PAS) of the enzyme. Here we present evidence for the structural motif of AChE involved in this interaction. First, we modeled the docking of A beta onto the structure of Torpedo californica AChE, and identified four potential sites for AChE-A be ta complex formation. One of these, Site I, spans a major hydrophobic seque nce exposed on the surface of AChE, which had been previously shown to inte ract with liposomes [Shin et al. (1996) Protein Sci. 5, 42-51]. Second, we examined several AChE-derived peptides and found that a synthetic 35-residu e peptide corresponding to the above hydrophobic sequence was able to promo te amyloid formation. We also studied the ability to promote amyloid format ion of two synthetic 24-residue peptides derived from the sequence of a Ome ga -loop, which has been suggested as an AChE-A beta interacting motif. Kin etic analyses indicate that only the 35-residue hydrophobic peptide mimics the effect of intact AChE on amyloid formation. Moreover, RP-HPLC analysis revealed that the 35-residue peptide was incorporated into the growing A be ta -fibrils. Finally, fluorescence binding studies showed that this peptide binds A beta with a K-d = 184 muM, independent of salt concentration, indi cating that the interaction is primarily hydrophobic. Our results indicate that the homologous human AChE motif is capable of accelerating A beta fibr illogenesis.