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Hierarchical Assembly Pathways of Spermine Induced Tubulin Conical-Spiral Architectures

preprint
revised on 13.01.2020 and posted on 14.01.2020 by Raviv Dharan, Asaf Shemesh, Abigail Millgram, Yael Levi-Kalisman, Israel Ringel, Uri Raviv

Tubulin, an essential cytoskeletal protein, assembles into various morphologies by interacting with cellular factors. Spermine, an endogenous polyamine, promotes and stabilizes tubulin assemblies. Yet, the assembled structures and their formation pathways are poorly known. Here we show that spermine induced tubulin to assemble in vitro into hierarchical architectures, based on a tubulin conical-spiral (TCS) subunit. Using solution X-ray scattering and cryo-TEM, we showed that with progressive increase of spermine concentration, tubulin-dimers assembled into a tubulin helical-pitch (or a short TCS), TCSs, TCS that stacked into tubes through base-to-top packing, antiparallel bundles of TCS tubes in a quasi-hexagonal symmetry, and eventually twisted hexagonal bundles of inverted tubulin tubules. Time-resolved experiments revealed that tubulin assemblies formed at low spermine concentrations were precursors of the assemblies formed at higher spermine concentrations. The results provide insight into the variety of morphologies that tubulin can form, and contribute to our understanding of the fundamental interactions that control the composition and construction of protein-based biomaterials.

Funding

Israel Ministry of Science

Israel Science Foundation (656/17)

United States-Israel Binational Science Foundation (2016311)

History

Email Address of Submitting Author

uri.raviv@mail.huji.ac.il

Institution

The Hebrew University of Jerusalem

Country

Israel

ORCID For Submitting Author

0000-0001-5992-9437

Declaration of Conflict of Interest

No conflict of Interest

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