Suchergebnisse

Background: Tau is a microtubule associated protein that regulates the stability of microtubules and the microtubule-dependent axonal transport. Its hyperphosphorylated form is one of the hallmarks of Alzheimer's disease and other tauopathies and the major component of the paired helical filaments that form the abnormal proteinaceous tangles found in these neurodegenerative diseases. It is generally accepted that the phosphorylation extent of tau is the result of an equilibrium in the activity of protein kinases and phosphatases. Disruption of the balance between both types of enzyme activities has been assumed to be at the origin of tau hyperphosphorylation and the subsequent toxicity and progress of the disease. Objective: We explore the possibility that, beside the phosphatase action on phosphorylated tau, the catalytic subunit of PKA catalyzes both tau phosphorylation and also tau dephosphorylation, depending on the ATP/ADP ratio. Methods: We use the shift in the relative electrophoretic mobility suffered by different phosphorylated forms of tau, as a sensor of the catalytic action of the enzyme. Results: The results are in agreement with the long-known thermodynamic reversibility of the phosphorylation reaction (ATP + Protein = ADP+Phospho-Protein) catalyzed by PKA and many other protein kinases. Conclusion: The results contribute to put the compartmentalized energy state of the neuron and the mitochondrial-functions disruption upstream of tau-related pathologies ; Financial support has been provided by a grant from the Spanish Government PGC2018 096177-B-100

Background: Tau is a microtubule associated protein that regulates the stability of microtubules and the microtubule-dependent axonal transport. Its hyperphosphorylated form is one of the hallmarks of Alzheimer's disease and other tauopathies and the major component of the paired helical filaments that form the abnormal proteinaceous tangles found in these neurodegenerative diseases. It is generally accepted that the phosphorylation extent of tau is the result of an equilibrium in the activity of protein kinases and phosphatases. Disruption of the balance between both types of enzyme activities has been assumed to be at the origin of tau hyperphosphorylation and the subsequent toxicity and progress of the disease. Objective: We explore the possibility that, beside the phosphatase action on phosphorylated tau, the catalytic subunit of PKA catalyzes both tau phosphorylation and also tau dephosphorylation, depending on the ATP/ADP ratio. Methods: We use the shift in the relative electrophoretic mobility suffered by different phosphorylated forms of tau, as a sensor of the catalytic action of the enzyme. Results: The results are in agreement with the long-known thermodynamic reversibility of the phosphorylation reaction (ATP + Protein = ADP+Phospho-Protein) catalyzed by PKA and many other protein kinases. Conclusion: The results contribute to put the compartmentalized energy state of the neuron and the mitochondrial-functions disruption upstream of tau-related pathologies. ; Spanish Government PGC2018 096177-B_100

Tau hyperphosphorylation can be considered as one of the hallmarks of Alzheimer's disease and other tauophaties. Besides its well-known role as a microtubule associated protein, Tau displays a key function as a protector of genomic integrity in stress situations. Phosphorylation has been proven to regulate multiple processes including nuclear translocation of Tau. In this contribution, we are addressing the physicochemical nature of DNA-Tau interaction including the plausible influence of phosphorylation. By means of surface plasmon resonance (SPR) we measured the equilibrium constant and the free energy, enthalpy and entropy changes associated to the Tau-DNA complex formation. Our results show that unphosphorylated Tau binding to DNA is reversible. This fact is in agreement with the protective role attributed to nuclear Tau, which stops binding to DNA once the insult is over. According to our thermodynamic data, oscillations in the concentration of dephosphorylated Tau available to DNA must be the variable determining the extent of Tau binding and DNA protection. In addition, thermodynamics of the interaction suggest that hydrophobicity must represent an important contribution to the stability of the Tau-DNA complex. SPR results together with those from Tau expression in HEK cells show that phosphorylation induces changes in Tau protein which prevent it from binding to DNA. The phosphorylation-dependent regulation of DNA binding is analogous to the Tau-microtubules binding inhibition induced by phosphorylation. Our results suggest that hydrophobicity may control Tau location and DNA interaction and that impairment of this Tau-DNA interaction, due to Tau hyperphosphorylation, could contribute to Alzheimer's pathogenesis. © 2014 Camero et al. ; Spanish Government and Comunidad de Madrid. CIBERNED (Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas ; Peer Reviewed

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. © 2014-IOS Press and the authors. All rights reserved. ; Spanish Government (SAF2006-02424 and SAF2010-15525) and Comunidad de Madrid (P2009/TIC-1476).