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The interaction of tau protein with other key proteins essential for stress granule formation determines their functional and pathological impact. In a biological framework, the synergy between Alzheimer's associated tau protein and the stress granule core protein TIA1 is widely recognized. However, the molecular details of this association remain unclear. In this study, we throw light on the importance of the state in which the TIA1 exists in mediating its association with the tau protein. Investigations were carried out on the three repeat constructs of tau (K19) and different structures formed by TIA1. Specifically, the condensate formed by TIA1 full-length (TIA1-FL) protein as well as fibril formed by low complexity domain of TIA1 (TIA1-LCD). The dynamics of K19 inside TIA1-FL condensates and the aggregation kinetics of K19 in the presence of TIA1-LCD fibrils were examined using various biophysical techniques. Relaxation-based solution NMR spectroscopic investigations suggest a weak interaction with TIA1 condensates and indicated a reduction in the dynamics of K19 within these TIA1 condensates. In contrast, a significant interaction was observed between K19, and TIA1-LCD fibrils primarily mediated through 321 KCGS 324 and 306 VQIVYKPVDLSKV 317 . Our findings emphasize that the interaction between Tau and TIA1 varies depending on whether TIA1 is in its physiological condensate form or its pathological fibril state.

The initial stages of amyloid fibrilization begin with the monomers populating aggregation-prone conformers. Characterization of such aggregation-prone conformers is crucial in the study of neurodegenerative diseases. The current study characterizes the aggregation pathway of two tau protein constructs that have been recently demonstrated to form Alzheimer's (AD) fibril structures with divalent ions and chronic traumatic encephalopathy (CTE) fibril structures with monovalent ions. The results highlight the involvement of identical residues in both the primary and secondary processes of both AD and CTE fibril propagation. Nuclear magnetic resonance relaxation experiments reveal increased flexibility of the motifs 321 KCGS within R3 and 364 PGGGN within R4 in the presence of MgCl 2 /NaCl, correlating with faster aggregation kinetics and indicating efficient primary nucleation. Notably, the seeded aggregation kinetics of the tau monomers in the presence and absence of metal ions are strikingly different. This correlates with the overall sign of the 15 N - Δ R 2 profile specifying the dominant mechanism involved in the process of aggregation.

The kinetochore establishes the linkage between chromosomes and the spindle microtubule plus ends during mitosis. In vertebrates, the spindle-kinetochore-associated (Ska1,2,3) complex stabilizes kinetochore attachment with the microtubule plus ends, but how Ska is recruited to and stabilized at the kinetochore-microtubule interface is not understood. Here, our results show that interaction of Ska1 with the general microtubule plus end-associated protein EB1 through a conserved motif regulates Ska recruitment to kinetochores in human cells. Ska1 forms a stable complex with EB1 via interaction with the motif in its N-terminal disordered loop region. Disruption of this interaction either by deleting or mutating the motif disrupts Ska complex recruitment to kinetochores and induces chromosome alignment defects, but it does not affect Ska complex assembly. Atomic-force microscopy imaging revealed that Ska1 is anchored to the C-terminal region of the EB1 dimer through its loop and thereby promotes formation of extended structures. Furthermore, our NMR data showed that the Ska1 motif binds to the residues in EB1 that are the binding sites of other plus end targeting proteins that are recruited to microtubules by EB1 through a similar conserved motif. Collectively, our results demonstrate that EB1-mediated Ska1 recruitment onto the microtubule serves as a general mechanism for the formation of vertebrate kinetochore-microtubule attachments and metaphase chromosome alignment., Competing Interests: Conflict of interest The authors declare no conflict of interest., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Different cryo-EM derived atomic models of in vivo tau filaments from patients with tauopathies consisted of R3 and R4 repeats of the microtubule-binding domain. In comparison, only the R3 repeat forms the core of the heparin-induced fibrils of the three repeat tau isoforms. For developing therapeutics, it is desirable to have an in vitro tau aggregation system producing fibrils corresponding to the disease morphology. Here we report the self-aggregation of truncated tau segment R3R4 peptide without requiring heparin for aggregation induction. We used NMR spectroscopy and other biophysical methods to monitor the self-aggregation of R3R4. We identified the hexapeptide region in R3 and β-turn region in R4 as the aggregation initiating region of the protein. The solid-state NMR of self-aggregated R3R4 fibrils demonstrated that in addition to R3 residues, residues of R4 were also part of the fibril filaments. The presence of both R3 and R4 residues in the aggregation process and the core of fibril filaments suggest that the aggregation of R3R4 might resemble the in vivo aggregation process., (© 2021 Wiley-VCH GmbH.)