Tau Protein Provides DNA with Thermodynamic and Structural Features which are Similar to those Found in Histone-DNA Complex

Tau protein has been proposed as a trigger of Alzheimer's disease once it is hyperphosphorylated. However, the role that native tau forms play inside the neuronal nucleus remains unclear. In this work we present results concerning the interaction of tau protein with double-stranded DNA, single-stranded DNA, and also with a histone-DNA complex. The tau-DNA interaction results in a structure resembling the beads-on-a-string form produced by the binding of histone to DNA. DNA retardation assays show that tau and histone induce similar DNA retardation. A surface plasmon resonance study of tau-DNA interaction also confirms the minor groove of DNA as a binding site for tau, similarly to the histone binding. A residual binding of tau to DNA in the presence of Distamycin A, a minor groove binder, suggests the possibility that additional structural domains on DNA may be involved in tau interaction. Finally, DNA melting experiments show that, according to the Zipper model of helix-coil transition, the binding of tau increases the possibility of opening the DNA double helix in isolated points along the chain, upon increasing temperature. This behavior is analogous to histones and supports the previously reported idea that tau could play a protective role in stress situations. Taken together, these results show a similar behavior of tau and histone concerning DNA binding, suggesting that post-translational modifications on tau might impair the role that, by modulating the DNA function, might be attributable to the DNA-tau interaction.