The reactivity of the C-terminal antibody shows differences possibly due to the changes in the global folds of tau isoforms

Lenka Hornakova1,2, Rostislav Skrabana1,3, Ondrej Cehlar1,3

1Institute of Neuroimmunology of Slovak Academy of Sciences, Dubravska cesta 9, 84510 Bratislava, Slovakia

2Faculty of Natural Sciences, Comenius University, Ilkovicova 6, 84215 Bratislava, Slovakia

3Axon Neuroscience R&D Services SE, Dvorakovo nabrezie 10, 81102 Bratislava, Slovakia

hornakova.lenka6@gmail.com

Alzheimer’s disease (AD) is the most common cause of dementia and thus a disease that radically reduces the quality of life not only for patient but also for the patient’s family. An important role in the development and progression of this disease is played by the accumulation of two proteins, namely the tau protein and β-amyloid, caused by changes in their structures.

The structural insights into the pathological and physiological tau protein conformations may help to answer the key questions of the pathogenesis of AD and other tauopathies. All isoforms of tau protein consist of four main domains and differ according to number of N-terminal inserts (0N, 1N, 2N) and microtubule binding repeat regions - MTBRs (3R, 4R). An important regulatory role is played by the C-terminal domain that has shown to have an inhibitory effect on tau pathological aggregation [1].

We have been studying the kinetics of the interaction between the antibody DC39C, which epitope lies inside the last 12 C-terminal amino acids of tau, and various tau proteins by surface plasmon resonance. According to recent insights into the structure of tau protein obtained by cross-linking mass spectrometry guided discrete molecular dynamics, where tau molecule was modelled as a rather globular and compact [2], the epitope of DC39C antibody should be hidden in between the beta strands of the first N-terminal insert and the N-terminus of tau protein. Global conformation that was previously observed by FRET method supports the model that places the C-terminal domain between the MTBRs and the N-terminal domain [3]. Our results have shown that isoforms without the N-terminal inserts bind to DC39C antibody better than isoforms containing them; same results were obtained when tau with various N-terminal domain truncation were used.

Subsequently, we have measured the kinetics of the heparin-induced filament formation by ThT fluorescence to observe the effect of the C-terminal domain removal on tau aggregation. We have compared the longest full length 3R tau isoform with two truncated tau proteins: tau151-391/3R which causes Alzheimer´s like pathology in the rat model [4] and the full length 3R tau isoform without the C-terminus (1-391/3R). The double truncated tau construct (151-391/3R) indicated very rapid filament formation; slightly slower filament formation was observed for tau protein without C-terminal, and the slowest filament formation was given by the isoform tau39 (2N3R). These findings also support the previously proposed hypothesis of C-terminal domain inhibition of tau aggregation.

1.     Abraha, A., Ghoshal, N., Gamblin, T. C., Cryns, V., Berry, R. W., Kuret, J. & Binder, L. I., J Cell Sci 113, (2000), 3737-3745.

2.     Popov, K. I., Makepeace, K. A. T., Petrotchenko, E. V., Dokholyan, N. V. & Borchers, C. H., Structure 27, (2019), 1710-1715 e1714.

3.     Jeganathan, S., von Bergen, M., Brutlach, H., Steinhoff, H. J. & Mandelkow, E., Biochemistry-Us 45, (2006), 2283-2293.

4.       Filipcik, P., Zilka, N., Bugos, O., Kucerak, J., Koson, P., Novak, P. & Novak, M., Neurobiol Aging 33, (2012) 1448-1456.

This work was supported by the Vega grant number 2/0145/19.