Fibril-forming motifs are essential and sufficient for the fibrillization of human Tau.

BACKGROUND: The misfolding of amyloidogenic proteins including human Tau protein, human prion protein, and human α-synuclein is involved in neurodegenerative diseases such as Alzheimer disease, prion disease, and Parkinson disease. Although a lot of research on such amyloidogenic proteins has been done, we do not know the determinants that drive these proteins to form fibrils and thereby induce neurodegenerative diseases. In this study, we want to know the role of fibril-forming motifs from such amyloidogenic proteins in the fibrillization of human Tau protein. METHODOLOGY/PRINCIPAL FINDINGS: As evidenced by thioflavin T binding and turbidity assays, transmission electron microscopy, and circular dichroism, fibril-forming motifs are essential and sufficient for the fibrillization of microtubule-associated protein Tau: only when both of its fibril-forming motifs, PHF6 and PHF6*, are deleted can recombinant human Tau fragment Tau(244-372) lose its ability to form fibrils, and the insertion of unrelated fibril-forming motifs from other amyloidogenic proteins, such as human prion protein, yeast prion protein, human α-synuclein, and human amyloid ß, into the disabled Tau protein can retrieve its ability to form fibrils. Furthermore, this retrieval is independent of the insertion location on Tau(244-372). CONCLUSIONS/SIGNIFICANCE: We demonstrate for the first time that insertion of fibril-forming motifs can replace PHF6/PHF6* motifs, driving human Tau protein to form fibrils with different morphologies and different kinetic parameters. Our results suggest that fibril-forming motifs play a key role in the fibrillization of human Tau protein and could be the determinants of amyloidogenic proteins tending to misfold, thereby causing the initiation and development of neurodegenerative diseases. Our study also touches on the importance of amyloid "strains": changes to the amyloidgenic driver region results in altered structural morphologies at the macromolecular level.

The contrasting effect of macromolecular crowding on amyloid fibril formation.

BACKGROUND: Amyloid fibrils associated with neurodegenerative diseases can be considered biologically relevant failures of cellular quality control mechanisms. It is known that in vivo human Tau protein, human prion protein, and human copper, zinc superoxide dismutase (SOD1) have the tendency to form fibril deposits in a variety of tissues and they are associated with different neurodegenerative diseases, while rabbit prion protein and hen egg white lysozyme do not readily form fibrils and are unlikely to cause neurodegenerative diseases. In this study, we have investigated the contrasting effect of macromolecular crowding on fibril formation of different proteins. METHODOLOGY/PRINCIPAL FINDINGS: As revealed by assays based on thioflavin T binding and turbidity, human Tau fragments, when phosphorylated by glycogen synthase kinase-3ß, do not form filaments in the absence of a crowding agent but do form fibrils in the presence of a crowding agent, and the presence of a strong crowding agent dramatically promotes amyloid fibril formation of human prion protein and its two pathogenic mutants E196K and D178N. Such an enhancing effect of macromolecular crowding on fibril formation is also observed for a pathological human SOD1 mutant A4V. On the other hand, rabbit prion protein and hen lysozyme do not form amyloid fibrils when a crowding agent at 300 g/l is used but do form fibrils in the absence of a crowding agent. Furthermore, aggregation of these two proteins is remarkably inhibited by Ficoll 70 and dextran 70 at 200 g/l. CONCLUSIONS/SIGNIFICANCE: We suggest that proteins associated with neurodegenerative diseases are more likely to form amyloid fibrils under crowded conditions than in dilute solutions. By contrast, some of the proteins that are not neurodegenerative disease-associated are unlikely to misfold in crowded physiological environments. A possible explanation for the contrasting effect of macromolecular crowding on these two sets of proteins (amyloidogenic proteins and non-amyloidogenic proteins) has been proposed.

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 ß-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 ß-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.