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Publication Abstract from PubMed

A critical feature of microtubules is their GTP cap, a stabilizing GTP-tubulin rich region at growing microtubule ends. Microtubules polymerized in the presence of GTP analogs or from GTP hydrolysis-deficient tubulin mutants have been used as GTP-cap mimics for structural and biochemical studies. However, these analogs and mutants generate microtubules with diverse biochemical properties and lattice structures, leaving it unclear what is the most faithful GTP mimic and hence the structure of the GTP cap. Here, we generate a hydrolysis-deficient human tubulin mutant, alphaE254Q, with the smallest possible modification. We show that alphaE254Q-microtubules are stable, but still exhibit mild mutation-induced growth abnormalities. However, mixing two GTP hydrolysis-deficient tubulin mutants, alphaE254Q and alphaE254N, at an optimized ratio eliminates growth and lattice abnormalities, indicating that these 'mosaic microtubules' are faithful GTP cap mimics. Their cryo-electron microscopy structure reveals that longitudinal lattice expansion, but not protofilament twist, is the primary structural feature distinguishing the GTP-tubulin containing cap from the GDP-tubulin containing microtubule shaft. However, alterations in protofilament twist may be transiently needed to allow lattice compaction and GTP hydrolysis. Together, our results provide insights into the structural origin of GTP cap stability, the pathway of GTP hydrolysis and hence microtubule dynamic instability.

Hydrolysis-deficient mosaic microtubules as faithful mimics of the GTP cap.,Estevez-Gallego J, Blum TB, Ruhnow F, Gili M, Speroni S, Garcia-Castellanos R, Steinmetz MO, Surrey T Nat Commun. 2025 Mar 10;16(1):2396. doi: 10.1038/s41467-025-57555-6. PMID:40064882^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.