Formation, regulation and dynamics of phase separated postsynaptic density condensates with Tau and Fyn
by Zheng Shen
Date of Examination:2023-12-19
Date of issue:2024-11-22
Advisor:Prof. Dr. Markus Zweckstetter
Referee:Prof. Dr. Tiago Fleming Outeiro
Referee:Prof. Dr. Silvio O. Rizzoli
Persistent Address:
http://dx.doi.org/10.53846/goediss-10895
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Abstract
English
Alzheimer’s disease is characterized by memory loss and cognitive impairments. The cognitive deficits and synaptic dysfunction are associated with the excitotoxicity mediated by NMDA (N-methyl-D-aspartate) receptors on the postsynaptic membrane. Increasing recent evidence suggests that the excessive activation of NMDA receptors is related to the postsynaptic accumulation of microtubule-associated protein Tau, which is regarded as a pathogenic protein in many neurodegenerative diseases collectively known as tauopathies. In addition, the postsynaptic recruitment of the tyrosine kinase Fyn has been associated with Tau-mediated synaptotoxicity in Alzheimer’s disease via Tau/Fyn direct interaction. However, the correlation between postsynaptic Tau and synaptic dysfunction, as well as the molecular basis of disease-associated Tau/Fyn interaction at the postsynaptic compartment remain elusive. Here, we show that full-length 2N4R Tau (called Tau hereafter) decreases the dynamics of phase-separated and liquid-like condensates biochemically reconstituted by the four major postsynaptic density proteins PSD-95, GKAP, Shank and Homer in solution, as well as NMDA receptor-associated protein clusters on synthetic lipid membranes. Tau-mediated droplet/cluster dynamic arrest critically depends on the multivalent interactions between Tau and a canonical GMP-binding pocket in the guanylate kinase domain of PSD-95, which is a major postsynaptic density scaffold protein directly binding and mediating the clustering of NMDA receptors. We further reveal that the competitive binding of a high-affinity phosphorylated peptide to PSD-95 rescues the diffusional dynamics of an NMDA truncated construct, which contains the last five amino acids of the NMDA receptor subunit NR2B fused to the C-terminus of the tetrameric GCN4 coiled-coil domain in postsynaptic density- like condensates/clusters. The disease-associated Y18-phosphorylated 2N4R Tau, which is phosphorylated by tyrosine kinase Fyn, further increase the number and size of postsynaptic density condensates, as well as exerting a larger dampening effect on the dynamics of condensates compared to wild-type Tau. Furthermore, we report that the proline-rich region and the first microtubule-binding repeat of Tau interact multivalently with the SH3 domain of Fyn. We present an atomic-resolution heterotrimeric structure of two SH3 domains of Fyn holding together with one P216/P219-containing Tau peptide. Moreover, we demonstrate that Tau and Fyn colocalize in phase-separated postsynaptic density condensates, where they promote the mutual trapping and dynamic arrest of each other. Taken together, our findings propose a molecular mechanism where Tau modulates the dynamic properties of the postsynaptic density, as well as establish a structural model underpinning neurotoxic Tau/Fyn interaction and clustering at the postsynaptic compartment.
Keywords: Tau; Postsynaptic Density; Biomolecular Condensates; Alzheimer's disease; Fyn
