Microtubules accelerate the kinase activity of Aurora-B by a reduction in dimensionality

• Published in: PloS one 2014-02, Vol.9 (2), p.e86786-e86786
• Main Authors: Noujaim, Michael, Bechstedt, Susanne, Wieczorek, Michal, Brouhard, Gary J
• Format: Article
• Language: English
• Subjects: Activation; Animals; Aurora Kinase B - chemistry; Aurora Kinase B - genetics; Aurora Kinase B - metabolism; Binding; Biology; Centromere - metabolism; Centromeres; Chromosomal Proteins, Non-Histone - genetics; Chromosomal Proteins, Non-Histone - metabolism; Chromosomes; Deoxyribonucleic acid; DNA; Electrophoresis, Polyacrylamide Gel; Electrostatic properties; Enzymatic activity; Enzyme Activation; Kinases; Kinetics; Localization; Microtubule-associated proteins; Microtubules - chemistry; Microtubules - metabolism; Models, Biological; Models, Molecular; Passengers; Phosphorylation; Polymerization; Protein Binding; Protein Structure, Tertiary; Proteins; Proteolysis; Random walk; Reduction; Saccharomyces cerevisiae; Salts; Scaffolding; Scaffolds; Substrate Specificity; Substrates; Tubulin; Xenopus; Xenopus laevis - genetics; Xenopus laevis - metabolism; Xenopus Proteins - chemistry; Xenopus Proteins - genetics; Xenopus Proteins - metabolism; Yeast
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0086786

Aurora-B is the kinase subunit of the Chromosome Passenger Complex (CPC), a key regulator of mitotic progression that corrects improper kinetochore attachments and establishes the spindle midzone. Recent work has demonstrated that the CPC is a microtubule-associated protein complex and that microtubules are able to activate the CPC by contributing to Aurora-B auto-phosphorylation in trans. Aurora-B activation is thought to occur when the local concentration of Aurora-B is high, as occurs when Aurora-B is enriched at centromeres. It is not clear, however, whether distributed binding to large structures such as microtubules would increase the local concentration of Aurora-B. Here we show that microtubules accelerate the kinase activity of Aurora-B by a "reduction in dimensionality." We find that microtubules increase the kinase activity of Aurora-B toward microtubule-associated substrates while reducing the phosphorylation levels of substrates not associated to microtubules. Using the single molecule assay for microtubule-associated proteins, we show that a minimal CPC construct binds to microtubules and diffuses in a one-dimensional (1D) random walk. The binding of Aurora-B to microtubules is salt-dependent and requires the C-terminal tails of tubulin, indicating that the interaction is electrostatic. We show that the rate of Aurora-B auto-activation is faster with increasing concentrations of microtubules. Finally, we demonstrate that microtubules lose their ability to stimulate Aurora-B when their C-terminal tails are removed by proteolysis. We propose a model in which microtubules act as scaffolds for the enzymatic activity of Aurora-B. The scaffolding activity of microtubules enables rapid Aurora-B activation and efficient phosphorylation of microtubule-associated substrates.