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Characterization of in vitro glycation sites of tau
1Department of Pathology, Albert Einstein College of Medicine, Bronx, New York 10461, U.S.A.
Abstract:
Tau is a microtubule-associated protein that loses microtubule binding activity and aggregates into paired helical filaments (PHFs) in Alzheimer's disease. Nonenzymic glycation is one of the posttranslational modifications detected in PHF-tau, but not in normal tau. PHF-tau has reduced ability to bind to microtubules. To determine whether glycation of tau occurs in its microtubule binding domains, we have characterized in vitro glycation sites of the longest isoform of tau, which has four microtubule binding domains (Tau-4). The identified glycation sites are Lys-87, 132, 150, 163, 174, 225, 234, 259, 280, 281, 347, 353, and 369. We have also studied glycation of another isoform of tau, which has only three microtubule binding domains (Tau-3). This isoform is modified by glucose 15-20% more slowly than Tau-4. However, the glycation sites appear to be the same in both isoforms, except for Lys-280 and 281; these are located in the second microtubule binding domain, which is missing in Tau-3. Lys-150, 163, and 174 are located within or proximal to the sequence of tau that is involved in the microtubule nucleation activity, and Lys-259, 280, 281, 347, 353, and 369 are located in the microtubule binding domains. Glycation at these sites can affect the functional properties of tau, and advanced glycation at these sites might lead to the formation of insoluble aggregates similar to the ones seen in Alzheimer's disease.
Insights
Nonenzymic glycation modifies tau protein in Alzheimer's disease, affecting its microtubule binding. This study identifies specific glycation sites in tau, potentially explaining its aggregation and reduced function in the disease.
Area of Science:
- Neuroscience
- Biochemistry
- Molecular Biology
Background:
- Tau is a microtubule-associated protein crucial for neuronal function.
- In Alzheimer's disease, tau detaches from microtubules and forms aggregates.
- Nonenzymic glycation is a modification found in aggregated tau but not normal tau.
Purpose of the Study:
- To investigate if tau glycation occurs within its microtubule-binding domains.
- To identify specific glycation sites on tau protein in vitro.
- To understand the potential impact of glycation on tau's function and aggregation.
Main Methods:
- In vitro characterization of glycation sites on tau isoforms (Tau-4 and Tau-3).
- Analysis of specific lysine residues modified by glucose.
- Comparison of glycation patterns between different tau isoforms.
Main Results:
- Identified 13 specific lysine residues as in vitro glycation sites on Tau-4.
- Tau-3 showed slower glucose modification compared to Tau-4.
- Glycation sites were located within or near microtubule binding and nucleation domains.
- Lys-280 and Lys-281 were notably absent in Tau-3 glycation sites.
Conclusions:
- Nonenzymic glycation targets specific sites in tau's microtubule-binding domains.
- Glycation of these sites may impair tau's ability to bind microtubules and nucleate assembly.
- Advanced glycation at these sites could contribute to the formation of insoluble tau aggregates observed in Alzheimer's disease.