Insights into the Alzheimer's disease specific pre-aggregation conformation of monomeric tau proteins using DC11 antibody

O. Cehlar1*, S. Njemoga1, R. Skrabana1, V. Volko2, J. Hritz2,3, P. Kaderavek2, B. Kovacech1

1 Institute of Neuroimmunology, Laboratory of Structural Biology of Neurodegeneration, Slovak

Academy of Sciences, Bratislava, Slovakia

2 CEITEC MU, Brno, Czech Republic

3Faculty of Science, Department of Chemistry, Masaryk University, Brno, Czech Republic

ondrej.cehlar@savba.sk


A key yet unresolved question of the pathogenesis of Alzheimer’s disease (AD) and other tauopathies is the cause and the mechanism of the transition from the unstructured monomeric tau protein to the insoluble filaments deposited in the brain tissue. 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 [1].

It was found that conformational antibodies DC11 and MN423 have catalytic pro-aggregatory effects in tau aggregation assay, whereas the antibody DC8E8 has inhibitory effects on tau filament formation [2]. 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. The information about conformatial epitopes of these antibodies are therefore of high significance.

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. However, previous studies suggest the importance of region 321-325 for the interaction of tau with DC11 antibody. We have further characterized the influence of DC11 Fab binding on the non-epitope tau residues using NMR relaxation measurements of 15N labelled tau dGAE.

The results highlight the importance of the R' region of tau, that was recently shown to be important also for tau interaction with microtubules [3]. This sequence forms the interface of rigid filament core and flanking fuzzy C terminal segment in solved tauopathy filaments.

1. Vechterova, L.; Kontsekova, E.; Zilka, N.; Ferencik, M.; Ravid, R.; Novak, M. Neuroreport, 14 (2003),87-91.

2. Kontsekova, E.; Zilka, N.; Kovacech, B.; Skrabana, R.; Novak, M. Alzheimers Res Ther, 6 (2014), 45.

3. El Mammeri, N., Dregni, A. J., Duan, P., Wang, H. K., Hong, M. Sci. Adv., 8 (2022), 4459.

Acknowledgment. This work was supported by research grants APVV 21-0479, VEGA 2/0125/23 and 2/0141/23, and by iNEXT-Discovery, grant number 871037, and MSCA-RISE 873127, both funded by the Horizon 2020 program of the European Commission.