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Calmodulin binds to a tubulin binding site of the microtubule-associated protein tau
R Padilla1, R B Maccioni, J Avila
1Centro de Bíologia Molecular, Universidad Autónoma, Madrid, Spain.
Abstract:
Previous studies have demonstrated that the microtubule-associated proteins MAP-2 and tau interact selectively with common binding domains on tubulin defined by the low-homology segments alpha (430-441) and beta (422-434). It has been also indicated that the synthetic peptide VRSKIGSTENLKHQPGGG corresponding to the first tau repetitive sequence represents a tubulin binding domain on tau. The present studies show that the calcium-binding protein calmodulin interacts with a tubulin binding site on tau defined by the second repetitive sequence VTSKCGSLGNIHHKPGGG. It was shown that both tubulin and calmodulin bind to tau peptide-Sepharose affinity column. Binding of calmodulin occurs in the presence of 1 mM Ca 2+ and it can be eluted from the column with 4 mM EGTA. These findings provide new insights into the regulation of microtubule assembly, since Ca2+/calmodulin inhibition of tubulin polymerization into microtubules could be mediated by the direct binding of calmodulin to tau, thus preventing the interaction of this latter protein with tubulin.
Insights
Calcium-binding protein calmodulin binds to the tau protein, a microtubule-associated protein. This interaction may regulate microtubule assembly by preventing tau from binding to tubulin.
Area of Science:
- Cell Biology
- Neuroscience
- Biochemistry
Background:
- Microtubule assembly is crucial for cellular functions.
- Microtubule-associated proteins (MAPs) like tau regulate microtubule dynamics.
- MAP-2 and tau share tubulin binding domains on alpha (430-441) and beta (422-434) low-homology segments.
Purpose of the Study:
- To investigate the interaction between calmodulin and the tau protein.
- To identify the specific binding site of calmodulin on tau.
- To elucidate the role of this interaction in regulating microtubule assembly.
Main Methods:
- Utilized tau peptide-Sepharose affinity chromatography.
- Investigated binding in the presence of calcium (Ca2+) and elution with EGTA.
- Characterized the binding site using a synthetic peptide representing the second tau repetitive sequence (VTSKCGSLGNIHHKPGGG).
Main Results:
- Calmodulin directly binds to tau at a site defined by the second repetitive sequence.
- Both tubulin and calmodulin bind to tau.
- Calmodulin binding to tau is calcium-dependent and can be reversed by EGTA.
Conclusions:
- Calmodulin interacts with a specific tubulin-binding site on tau.
- Ca2+/calmodulin can inhibit tubulin polymerization by binding to tau.
- This mechanism provides new insights into the regulation of microtubule assembly.