lansky & braun lab

Biophysics of Protein Ensemble Dynamics

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January 18, 2019 – Paper on formation of microtubule doublets

Microtubule doublets, consisting of an incomplete B-microtubule at the surface of a complete A-microtubule, provide a structural scaffold mediating intraflagellar transport and ciliary beating. Despite the fundamental role of microtubule doublets, the molecular mechanism governing their formation is unknown. We used a cell-free assay to demonstrate a crucial inhibitory role of the carboxyl-terminal tail of tubulin in microtubule doublet assembly. Removal of the carboxyl-terminal tail of an assembled A-microtubule allowed for the nucleation of a B-microtubule on its surface. Carboxyl-terminal tails of only one A-microtubule protofilament inhibited this side-to-surface tubulin interaction, which would be overcome in vivo with binding protein partners. The dynamics of B-microtubule nucleation and its distinctive isotropic elongation was elucidated by using live imaging. Thus, inherent interaction properties of tubulin provide a structural basis driving flagellar MTD assembly.

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September 22, 2018 – Preprint on phase separation of tau

Kinetically distinct phases of tau on microtubules regulate kinesin motors and severing enzymes

Tau is an intrinsically disordered protein, which diffuses on microtubules. In neurodegenerative diseases collectively termed tauopathies, tau malfunction and its detachment from axonal microtubules is correlated with microtubule degradation. It is known that tau can protect microtubules from microtubule-degrading enzymes, such as katanin. However, how tau can fulfill such regulative function is still unclear. Using in vitro reconstitution, we here show that tau molecules on microtubules cooperatively form islands of an ordered layer with regulatory qualities distinct from a comparably dense layer of diffusible tau. These islands shield the microtubules from katanin and kinesin-1 but are penetrable by kinesin-8 which causes the islands to disassemble. Our results indicate a new phase of tau, constituting an adjustable protective sheath around microtubules.

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