FAD-deficient P187S mutation of NAD(P)H:quinone oxidoreductase 1 (NQO1*2) binds and accelerates β-amyloid aggregation

Alzheimer's disease (AD) is one of the most prominent neurodegenerative diseases. Results from animal and cellular models suggest that FAD-deficient forms of NAD(P)H quinone oxidoreductase 1 (NQO1) may accelerate the aggregation of Alzheimer's amyloid-beta peptide (A beta(1-42)). Here, we examined in vitro whether NQO1 and its FAD-deficient P187S mutation (NQO1*2) directly interact with A beta(1-42) and modify its rate of aggregation. When monitored using the fluorescence of either noncovalent thioflavin T (ThT) or HiLyte Fluor 647 (HF647) dye covalently attached to the A beta(1-42) peptide, the aggregation kinetics of A beta(1-42) were markedly more rapid in the presence of NQO1*2 than the wild-type (WT) 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 that binds near the FAD-binding site and stabilizes NQO1*2, markedly decreased the aggregation kinetics of A beta(1-42). Imaging flow cytometry confirmed in-vitro coaggregation of NQO1 isoforms and A beta(1-42). A beta(1-42) alone forms rod-shaped fibril structures while in the presence of NQO1 isoforms, A beta(1-42) is incorporated in the middle of larger globular protein aggregates surrounded by NQO1 molecules. Isothermal titration calorimetry (ITC) analysis indicates that A beta(1-42) 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 coaggregates of A beta(1-42) and NQO1 isoforms and the potential relevance of FAD-deficient forms of NQO1 for amyloid aggregation diseases.