Speaker
Description
A key yet unresolved question of the pathogenesis of Alzheimer’s disease (AD) and other tauopathies is the mechanism of the transition from the unstructured monomeric tau protein to the insoluble filaments. In the physiological state, tau protein exists as a conformational ensemble of interconverting structures and on the scale of transition from monomeric through oligomeric and filamentous species we can observe conformations reacting with specific antibodies, mainly with DC11, which is able to specifically discriminate between tau proteins isolated from healthy brain and tau proteins isolated from the brain of AD patient. The antibody recognizes also the recombinant truncated tau proteins up to the shortest fragment tau321-391.
It was found that conformational antibody DC11 has a catalytic pro-aggregatory effects in tau aggregation assay. This may imply possible mechanism of induction of pathological tau conformation, in which the antibody prepared against pathological tau imprints the pathological conformation into the physiological tau proteins in solution and therefore speeds up the tau aggregation.
To further uncover the binding mode of the conformational antibody DC11, we have performed NMR epitope mapping using 13C, 15N labelled tau321-391 and tau297-391 (dGAE) and recombinantly prepared Fab fragment of DC11 antibody. The overlay of HSQC spectra showed the region of tau between residues 370-390 to be affected by the binding of DC11, i.e. its C-terminal region. The results were corroborated using hydrogen deuterium exchange mass spectrometry.
We have solved the X-ray structure of DC11 Fab fragment to a resolution of 1.33 Å crystallized in a space group P 1 21 1 and deposited it into the PDB database with PDB ID 9H8H. We have also obtained crystals of DC11 Fab and crystals of tentative complexes between DC11 and either tau321-391 or tau peptide tau371-387 in different space groups (Table 1). We have further measured the synchrotron SAXS data to characterize the conformational ensembles of tau297-391 (dGAE), tau316-391 and tau321-391 and in both batch and SEC-SAXS modes and of dGAE oligomers. We have also attempted to characterize the complexes between tau proteins and DC11 Fab fragment.
DC11 binds also oligomeric and fibrillar tau forms. Tau oligomers are thought to be the most toxic species in the pathogenesis of AD, however, intermediate fibrils were observed early in the course of aggregation reaction of truncated tau dGAE by cryo-EM.
We have performed docking and MD simulation of DC11 Fab fragment with tau peptide, tau oligomer and tau protofibril to further uncover the binding mode of DC11 antibody and shed light on the tau pre-aggregation conformation. We have also docked a set of 27 previously described tau aggregation inhibitors into the structures of coarse-grained MD obtained dimers of tau321-391.
Acknowledgements
This research was funded by APVV SK-BG-25-0031, VEGA 2/0125/23, 1/0825/25 and Horizon Europe 101087124.
