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Repeat motifs of tau bind to the insides of microtubules in the absence of taxol

By Santwana Kar, Juan Fan, Michael J. Smith, Michel Goedert and Linda A. Amos


The tau family of microtubule-asssociated proteins has a microtubule-binding domain which includes three or four conserved sequence repeats. Pelleting assays show that when tubulin and tau are co- assembled into microtubules, the presence of taxol reduces the amount of tau incorporated. In the absence of taxol, strong binding sites for tau are filled by one repeat motif per tubulin dimer; additional tau molecules bind more weakly. We have labelled a repeat motif with nanogold and used three-dimensional electron cryomicroscopy to compare images of microtubules assembled with labelled or unlabelled tau. With kinesin motor domains bound to the microtubule outer surface to distinguish between α- and β-tubulin, we show that the gold label lies on the inner surface close to the taxol binding site on β-tubulin. Loops within the repeat motifs of tau have sequence similarity to an extended loop which occupies a site in α-tubulin equivalent to the taxol-binding pocket in β-tubulin. We propose that loops in bound tau stabilize microtubules in a similar way to taxol, although with lower affinity so that assembly is reversible

Topics: Articles
Publisher: Oxford University Press
Year: 2003
DOI identifier: 10.1093/emboj/cdg001
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Provided by: PubMed Central
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