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Tau and HMW microtubule-associated proteins have different microtubule binding sites in vivo
Abstract:
We have previously demonstrated the immunofluorescent localization of the tau and HMW MAPS on microtubules in vivo. When cells were treated with the non-ioni detergent triton before fixation, however treated with the non-ionic detergent triton before fixation, however, the immunofluorescent staining of microtubules with antiserum to HMW protein disappears, while the staining with anti-tubulin of anti-tau serum remains unaffected. Because of these differences in sensitivity to triton, we conclude that tau protein and HMW protein have different binding sites on microtubules. Parallel ultrastructural studies indicate that this loss of staining correlates with a loss of filamentous projections from the outer wall of cytoplasmic microtubules. These results indicate that in vivo the HMW protein is most probably distributed along the outer surface of the microtubule as filamentous projections similar to those observed in vitro. The in vivo distribution of the HMW protein suggests that it may form part of the microtrabecular system and be involved in the interaction of microtubules with other cell organelles.
Insights
High molecular weight (HMW) MAPs and tau protein bind differently to microtubules in vivo. HMW MAPs are located on the outer surface, suggesting roles in organelle interactions.
Area of Science:
- Cell Biology
- Neuroscience
- Biochemistry
Background:
- Microtubules are essential cytoskeletal components involved in intracellular transport and structure.
- Microtubule-associated proteins (MAPs) regulate microtubule dynamics and interactions.
- Tau protein and High Molecular Weight MAPs (HMW MAPs) are key MAPs found in vivo.
Purpose of the Study:
- To investigate the distinct binding sites and in vivo localization of tau protein and HMW MAPs on microtubules.
- To determine the relationship between HMW MAP distribution and microtubule structure.
Main Methods:
- Immunofluorescent localization of tau and HMW MAPs on microtubules in fixed cells.
- Differential detergent extraction using Triton X-100 to assess protein binding sensitivity.
- Ultrastructural analysis to correlate protein loss with morphological changes.
Main Results:
- Triton X-100 treatment solubilized HMW MAPs, while tau protein and tubulin remained associated with microtubules.
- Loss of HMW MAP staining correlated with the disappearance of filamentous projections from the microtubule surface.
- In vivo localization of HMW MAPs was consistent with outer surface filamentous projections.
Conclusions:
- Tau protein and HMW MAPs exhibit differential binding affinities and locations on microtubules.
- HMW MAPs are likely situated on the external surface of microtubules in vivo.
- HMW MAPs may contribute to the microtrabecular network and mediate microtubule interactions with other organelles.