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Modification of tau to an Alzheimer's type protein interferes with its interaction with microtubules
C González1, G Farías, R B Maccioni
1Laboratory of Cellular and Molecular Biology, Faculty of Sciences, University of Chile, Santiago.
Abstract:
The microtubule associated protein tau is the main structural component of paired helical filaments (PHFs), aberrant polymers found intracellularly in neurons of brains with the Alzheimer's disease. Glycation is one of the posttranslational modifications that has been found in tau from PHFs, but not in normal brain tau. Studies were carried out with purified tau protein subjected to chemical modifications, in order to further investigate the mechanisms of tau self-association into PHFs. Tau was subjected to modifications affecting reactive lysyl residues, e.g., carbamoylation with potassium cyanate and glycation reaction with glucose. The effects of these modifications to produce functional alterations in tau capacity to bind brain tubulin and to induce microtubule assembly were investigated. Chemically-modified tau and tau of Alzheimer's type exhibited a similar microtubule interaction behavior as analysed by overlay assays, but those were different than normal tau controls. On the other hand, studies of the microtubule assembly kinetics indicated that the reported tau modifications resulted in a loss of its capacity to promote microtubule assembly from purified tubulin preparations. The data on the differences in the electrophoretic profiles, Western blots and the overlay patterns, along with those on the microtubule polymerisation of normal brain tau as compared with both modified and Alzheimer's tau, suggest changes in the functional behavior of this protein as a result of its structural modifications. These studies were complemented with an immunogold analysis at the electron microscope level, which indicated that the modified tau did not incorporate into assembled microtubules. These findings, combined with the results on tau chemical modifications suggest that the reactive lysine residues within functional domains on tau, e.g., those of the repetitive binding motifs, were affected by these modifications. Furthermore, these observations provide new clues to understand the anomalous interactions of tau in Alzheimer's disease.
Insights
Chemical modifications to tau protein, like glycation, impair its ability to bind tubulin and assemble microtubules. This suggests structural changes in tau contribute to its abnormal behavior in Alzheimer's disease.
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Tau protein is a key component of paired helical filaments (PHFs) in Alzheimer's disease (AD).
- Glycation, a posttranslational modification, is found in AD tau but not normal tau.
- Understanding tau's self-association mechanisms is crucial for AD research.
Purpose of the Study:
- To investigate how chemical modifications affect tau protein's function.
- To explore the role of reactive lysyl residues in tau self-association and PHF formation.
- To compare the behavior of modified tau with normal and Alzheimer's-type tau.
Main Methods:
- Purified tau protein was chemically modified (carbamoylation, glycation).
- Functional alterations in tau's binding to tubulin and microtubule assembly were assessed.
- Techniques included overlay assays, microtubule assembly kinetics, Western blots, and immunogold electron microscopy.
Main Results:
- Chemically modified tau and Alzheimer's-type tau showed similar microtubule interaction patterns.
- Modified tau lost its capacity to promote microtubule assembly.
- Electron microscopy revealed modified tau did not incorporate into assembled microtubules.
Conclusions:
- Structural modifications, particularly affecting reactive lysyl residues, alter tau's functional behavior.
- These modifications impact tau's ability to bind tubulin and assemble microtubules.
- Findings offer insights into aberrant tau interactions in Alzheimer's disease.