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bioRxiv · 10.1101/2024.01.29.577855

Cryo-EM structures of the tubulin cofactors reveal the molecular basis for the biogenesis of alpha/beta-tubulin

Taheri, A.·Wang, Z.·Singal, B.·Guo, F.·Al-Bassam, J.
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Abstract

Microtubule polarity and dynamic polymerization originate from the self-association properties of the a-tubulin heterodimer. For decades, it has remained poorly understood how the tubulin cofactors, TBCD, TBCE, TBCC, and the Arl2 GTPase mediate a-tubulin biogenesis from - and {beta}-tubulins. Here, we use cryogenic electron microscopy to determine structures of tubulin cofactors bound to {beta}-tubulin. These structures show that TBCD, TBCE, and Arl2 form a heterotrimeric cage-like TBC-DEG assembly around the a-tubulin heterodimer. TBCD wraps around Arl2 and almost entirely encircles -tubulin, while TBCE forms a lever arm that anchors along the other end of TBCD and rotates -tubulin. Structures of the TBC-DEG-{beta}-tubulin assemblies bound to TBCC reveal the clockwise rotation of the TBCE lever that twists a-tubulin by pulling its C-terminal tail while TBCD holds -tubulin in place. Altogether, these structures uncover transition states in {beta}-tubulin biogenesis, suggesting a vise-like mechanism for the GTP-hydrolysis dependent a-tubulin biogenesis mediated by TBC-DEG and TBCC. These structures provide the first evidence of the critical functions of the tubulin cofactors as enzymes that regulate the invariant organization of {beta}-tubulin, by catalyzing - and {beta}-tubulin assembly, disassembly, and subunit exchange which are crucial for regulating the polymerization capacities of {beta}-tubulins into microtubules.

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Taheri, A., Wang, Z., Singal, B., Guo, F., Al-Bassam, J.. 2024-01-31. Cryo-EM structures of the tubulin cofactors reveal the molecular basis for the biogenesis of alpha/beta-tubulin. https://doi.org/10.1101/2024.01.29.577855

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