Understanding molecular features of aggregation-resistant tau conformer using oxidized monomer

BackgroundAggregation of tau into paired helical filament (PHF) is a hallmark of Alzheimer's disease (AD), and Cys-mediated disulfide bond formation plays a vital role in tau fibrillation. While intermolecular disulfide bond between Cys residues in microtubule-binding repeat (MTBR) region facilitates tau aggregation, intramolecular disulfide bond attenuates the same, though the molecular basis for such phenomenon remains obscure. Thus intramolecular disulfide-bonded tau monomer might be an excellent model to understand the unique features of aggregation-resistant tau conformer.MethodsWe synthesized the Cys cross-linked tau40 monomer by oxidation and characterized the altered conformational dynamics in the molecule by Hydrogen-deuterium exchange, limited proteolysis and fluorescence quenching.ResultsDeuterium exchange study showed that rigidity was imparted in the core PHF region of oxidized tau40 in MTBR segment, consisting of the fundamental PHF6 motif. Conformational rigidity was prominent in C-terminal tail region also. Limited proteolysis supported reduced accessibility of MTBR region in the molecule.ConclusionsPHF formation of oxidized tau40 might be attenuated either by induction of intramolecular H-bonding between the regions of high β-structure propensity in second and third MTBR (R₂, R₃), thus preventing intermolecular interaction between them, or by imparted rigidity in R₂–R₃, preventing the formation of extended β-structure preceding fibrillation. Data indicated plausible effect of conformational adaptation on the nucleation process of oxidized tau40 assembly.General significanceOur findings unravel the essential molecular features of aggregation-resistant tau conformer. Therapeutics stabilizing such conformers in vivo might be of high benefit in arresting tau assembly during AD and other tauopathies.