Multiple and Alternative Sites Make Tau Protein an Adaptable Sticky Surface for the SH3 Domain of Fyn Kinase

The interaction between the microtubule associated protein Tau and the tyrosine kinase Fyn is believed to play a pivotal role in the early stage of Alzheimer's disease. Previous studies have identified the SRC Homology 3 (SH3) domain of Fyn as the binding receptor of several proline-rich motifs in Tau. However, the role of each proline-rich motif and their interplay in molecular recognition are still unclear. In this work, we investigated the mechanism of Fyn-SH3 recognition by the multiple PxxP sites inserted within the full-length Tau protein by using nuclear magnetic resonance (NMR) spectroscopy combined with computational, calorimetric and in-cell FRET (Förster resonance energy transfer) methods. Both in vitro and in-cell experiments revealed no single binding site strictly necessary for the binding. Instead, Fyn-SH3 contacts full-length Tau on multiple hot spot regions, located over a distance of 85 residues, through global moderate-to-low affinity interactions. Beyond two principal regions containing classical PxxP motifs, we identified a novel non-canonical binding site at the beginning of the microtubule binding domain. Our study indicates that multiple binding sites in Tau are involved in the interaction, making Tau an adaptable recognition surface that can function when single consensus motifs are deleted.