Fibrillization of Human Tau is Accelerated by Exposure to Lead Via Interaction with His-330 and His-362

Background: Neurofibrillary tangles, mainly consisted of bundles of filaments formed by the microtubule-associated protein Tau, are a hallmark of Alzheimer disease. Lead is a potent neurotoxin for human being especially for the developing children, and Pb(2+) at high concentrations is found in the brains of patients with Alzheimer disease. However, it has not been reported so far whether Pb(2+) plays a role in the pathology of Alzheimer disease through interaction with human Tau protein and thereby mediates Tau filament formation. In this study, we have investigated the effect of Pb(2+) on fibril formation of recombinant human Tau fragment Tau(244-372) and its mutants at physiological pH.

Methodology/principal Findings: As revealed by thioflavin T and 8-anilino-1-naphthalene sulfonic acid fluorescence, the addition of 5-40 µM Pb(2+) significantly accelerates the exposure of hydrophobic region and filament formation of wild-type Tau(244-372) on the investigated time scale. As evidenced by circular dichroism and Fourier transform infrared spectroscopy, fibrils formed by wild-type Tau(244-372) in the presence of 5-40 µM Pb(2+) contain more β-sheet structure than the same amount of fibrils formed by the protein in the absence of Pb(2+). However, unlike wild-type Tau(244-372), the presence of 5-40 µM Pb(2+) has no obvious effects on fibrillization kinetics of single mutants H330A and H362A and double mutant H330A/H362A, and fibrils formed by such mutants in the absence and in the presence of Pb(2+) contain similar amounts of β-sheet structure. The results from isothermal titration calorimetry show that one Pb(2+) binds to one Tau monomer via interaction with His-330 and His-362, with sub-micromolar affinity.

Conclusions/significance: We demonstrate for the first time that the fibrillization of human Tau protein is accelerated by exposure to lead via interaction with His-330 and His-362. Our results suggest the possible involvement of Pb(2+) in the pathogenesis of Alzheimer disease and provide critical insights into the mechanism of lead toxicity.