Tubulin Tails are Intrinsically Disordered Polyanions that Regulate Binding to other Proteins by Sequence as Well as Charge

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Microtubules (MT) are built by polymerization of the alpha/beta tubulin heterodimer. The two tubulins are very similar to each other and are composed of a globular body containing about 95% of the protein mass and an unstructured C-terminal tail (CTT) that contains about 40% of the protein's net negative charge. The CTT is the locus of most sequence differences between tubulin isotypes and also the target of most posttranslational modifications (PTMs). The tails extend from the tubulin body and from the outside surface of MT, and are often the first part of tubulin / MT that other proteins encounter. The high charge density on the tails can promote or oppose interaction interactions with other proteins. Surprisingly, perhaps, interactions with some proteins requires the negative charges, but are still highly modulated by sequence differences between tails from different isotypes. PTMs can add an additional, significant modulation of binding that can be determinative. Specific examples of each of these will be presented and discussed in the context of: Intrinsically Disordered Tails are Not Just Charged Strings.