High-Resolution Microtubule Structures Reveal the Structural Transitions in αβ-Tubulin upon GTP Hydrolysis

An expanded lattice is common to microtubules stabilized by different means, including Taxol, GMPCPP, and hydrolysis-deficient tubulin.

“Indeed, an expanded lattice is common to MTs stabilized by different means (Taxol, guanosine-5'-[(α,β)-methyleno]triphosphate [GMPCPP]), and hydrolysis-deficient tubulin; LaFrance et al., 2022; Alushin et al., 2014).”

Mammalian tubulin within the GDP lattice primarily adopts a compacted state, whereas newly incorporated GTP tubulin adopts an expanded state.

“Mammalian tubulin within the GDP lattice primarily adopts compacted state, whereas the newly incorporated GTP tubulin adopts an expanded state1.”

Taxanes induce the expanded microtubule lattice conformation.

“This expanded conformation, characterized by an increased longitudinal spacing between tubulin dimers, is also induced by taxanes 39-41 .”

The expanded microtubule lattice conformation is characterized by an increased longitudinal spacing between tubulin dimers.

“This expanded conformation, characterized by an increased longitudinal spacing between tubulin dimers, is also induced by taxanes 39-41 .”

Paclitaxel expands the microtubule lattice in the longitudinal direction.

“Paclitaxel is known to expand the microtubule lattice in the longitudinal direction 40,66 , an effect that could be readily observed by imaging microtubules sparsely labelled by fluorescent tubulin (Fig. 4g,i).”

The conformational change in microtubule lattice mostly affects the interface around the exchangeable nucleotide E-site of β-tubulin.

“This conformational change in microtubule lattice mostly affects the interface around the exchangeable nucleotide E-site of β-tubulin (Extended Data Fig. 6c) 40 .”

The Taxol-induced expansion observed in vitro (41.2-42.0 Å) is considerably smaller than the average hyper-expansion of 42.6 Å measured in situ.

“Remarkably, the Taxol-induced expansion to 41.2–42.0 Å observed in vitro (Alushin et al., 2014; Estevez-Gallego et al., 2020; Kellogg et al., 2017; Rai et al., 2020; Vale et al., 1994) is considerably smaller than the average hyper-expansion of 42.6 Å measured using our in situ approach.”

The GDP-bound state makes up the bulk of the microtubule shaft and is generally characterized by a compacted average monomer spacing of ∼41 Å.

“This GDP-bound state, which makes up the bulk of the microtubule shaft, generally is characterized by a compacted average monomer spacing of ∼41 Å that is distinct from that of the presumed GTP-bound state at the tip (the GTP-cap).”

Taxol expands the microtubule lattice longitudinally, increasing the dimer rise by approximately 2 Å.

“the addition of Taxol, the only treatment that altered the localization of StableMARK, is known to expand the MT lattice longitudinally, increasing the dimer rise by ∼2 Å (Alushin et al., 2014).”

The extent of tau-induced lattice compaction (3.2 ± 1.0%) is similar to the length difference between GTP- and GDP-bound tubulin dimers estimated previously by cryo-EM to be 2.4%.

“The extent of the compaction is similar to the length difference between GTP- and GDP-bound tubulin dimers estimated previously by cryo-EM to be 2.4%1”

PTXL binding likely allosterically remodels the tubulin interdimer interface, resulting in longitudinal MT expansion.

“It is likely that PTXL binding to the MT allosterically remodels the tubulin interdimer interface [57], resulting in longitudinal MT expansion [58].”

Measured axial repeat distances correspond closely to canonical compact and expanded lattice parameters reported in vitro and in intact cells.

“The measured axial repeat distances correspond closely to canonical compact and expanded lattice parameters reported in vitro45–47 and in intact cells48.”

Measured axial spacings match the well-established expanded (83 Å) and compact (81 Å) lattice spacing described for in vitro reconstituted microtubules.

“The measured axial spacings match the well-established expanded (83 Å) and compact (81 Å) lattice spacing described for in vitro reconstituted microtubules45–47.”

The classical view describes newly polymerized plus ends, where GTP-tubulin is incorporated and subsequently hydrolyzed as microtubules mature.

“This classical view describes newly polymerized plus ends, where GTP-tubulin is incorporated and subsequently hydrolyzed as the microtubules mature45,50,51.”

Microtubule lattice spacing has classically been linked to nucleotide state, with expanded lattices associated with GTP-like states and compact lattices associated with GDP-tubulin.

“Microtubule lattice spacing has classically been linked to nucleotide state, with expanded lattices associated with GTP-like states and compact lattices associated with GDP-tubulin45,50,51.”