Alzheimer's disease is one of the most prominent neurodegenerative diseases. Results from animal and cellular models suggest that FAD-deficient forms of NQO1 may accelerate the aggregation of Alzheimer's amyloid beta peptide Ab1-42. Here we examined in-vitro whether NQO1 and its FAD-deficient P187S mutation (NQO1*2) directly interact with Ab1-42 and modify its rate of aggregation. When monitored using the fluorescence of either non-covalent thioflavin T or HiLyte Fluor 647 dye covalently attached to the Ab1-42 peptide, the aggregation kinetics of Ab1-42 were markedly more rapid in the presence of NQO1*2 than the wild-type NQO1. Experiments using apo-NQO1 indicate that this increase is linked to the inability of... More
Alzheimer's disease is one of the most prominent neurodegenerative diseases. Results from animal and cellular models suggest that FAD-deficient forms of NQO1 may accelerate the aggregation of Alzheimer's amyloid beta peptide Ab1-42. Here we examined in-vitro whether NQO1 and its FAD-deficient P187S mutation (NQO1*2) directly interact with Ab1-42 and modify its rate of aggregation. When monitored using the fluorescence of either non-covalent thioflavin T or HiLyte Fluor 647 dye covalently attached to the Ab1-42 peptide, the aggregation kinetics of Ab1-42 were markedly more rapid in the presence of NQO1*2 than the wild-type NQO1. Experiments using apo-NQO1 indicate that this increase is linked to the inability of NQO1*2 to bind to FAD. Furthermore, dicoumarol, an NQO1 inhibitor which binds near the FAD binding site and stabilizes NQO1*2, markedly decreased the aggregation kinetics of Ab1-42. Imaging flow cytometry confirmed in-vitro co-aggregation of NQO1 isoforms and Ab1-42. Ab1-42 alone forms rod shaped fibril structures while in the presence of NQO1 isoforms, Ab1-42 is incorporated in the middle of larger globular protein aggregates surrounded by NQO1 molecules. Isothermal titration calorimetry analysis indicates that Ab1-42 interacts with NQO1 isoforms with a specific stoichiometry through a hydrophobic interaction with positive enthalpy and entropy changes. These data define the kinetics, mechanism, and shape of co-aggregates of Ab1-42 and NQO1 isoforms and the potential relevance of FAD-deficient forms of NQO1 for amyloid aggregation diseases.
