Alternative conformations of the Tau repeat domain in complex with an engineered binding protein

Area of Science:

• Neuroscience
• Biochemistry
• Structural Biology

Background:

• Tau protein aggregation into paired helical filaments is central to Alzheimer disease pathogenesis.
• This aggregation involves conformational changes in the Tau repeat domain, forming cross-β-structures characteristic of amyloid fibrils.

Purpose of the Study:

• To select and characterize a novel engineered binding protein, TP4, targeting the Tau repeat domain.
• To elucidate the binding sites and mechanism by which TP4 interacts with Tau and inhibits its aggregation.

Main Methods:

• Phage display was used to select TP4 against a Tau repeat domain construct (K18ΔK280).
• Nanomolar affinity binding of TP4 to Tau constructs was assessed.
• Nuclear Magnetic Resonance (NMR) spectroscopy was employed to identify TP4-binding sites within the Tau repeat domain.

Main Results:

• TP4 demonstrated nanomolar binding affinity for both K18ΔK280 and the full-length human Tau isoform (hTau40).
• NMR identified two distinct binding sites for TP4 within the Tau repeat domain, both containing aggregation-prone hexapeptide motifs (PHF6, PHF6*, PHF6**).
• TP4 effectively inhibited Tau aggregation at substoichiometric concentrations, indicating interference with the nucleation phase.

Conclusions:

• The engineered protein TP4 specifically targets key aggregation-prone regions within the Tau repeat domain.
• TP4's inhibition of Tau aggregation highlights its potential as a therapeutic agent for neurodegenerative diseases.
• This study provides detailed residue-level understanding of Tau-inhibitor interactions and reveals Tau's structural flexibility.