Polymerization of tau protein and the deposition of insoluble tau lesions highly correlate with the cognitive decline in Alzheimer’s disease and related tauopathies [1]. The most probable nuclei of tau protein aggregation are the hexapeptides VQIINK, VQIVYK and other two segments, each localized in one of the microtubule-binding repeats of tau [2, 3]. Recently we have described an anti-tau monoclonal antibody, DC8E8, which effectively blocked tau-tau interaction by binding four highly homologous epitopes in the immediate vicinity of aggregation-promoting hexapeptides [4]. The sequence of DC8E8 epitope served as a base for the construction of an active vaccine, which is currently under clinical development [5].
In the present study we aimed to answer the questions about the sequence and structure requirements of DC8E8-based immunomodulation. We have determined the kinetics of DC8E8 binding to each of its four binding sites on the tau protein molecule. Further, we have crystallized DC8E8 Fab fragment and its complexes with several tau peptides and solved the structure by X-ray crystallography. Finally, we validated our structural findings by alanine-scanning mutagenesis of DC8E8 paratope residues to confirm antibody contact sites. Obtained results allowed mechanistic insights into DC8E8 inhibitory activity.