Heterogeneous local structures of the microtubule lattice revealed by cryo-ET and non-averaging analysis

Microtubule cytoskeletons play pivotal roles in various cellular processes, including cell division and locomotion, by dynamically changing their length and distribution in cells through tubulin polymerization/depolymerization. Recent structural studies have revealed the polymorphic lattice structure of microtubules closely correlate with the microtubule dynamics, but the studies were limited to averaged structures. To reveal the transient and localized structures, such as GTP-cap, we developed several non-averaging methods for cryogenic electron tomography to precisely measure the longitudinal spacing and helical twisting of individual microtubule lattices at the tubulin subunit level. Our analysis revealed that polymerizing and depolymerizing ends share a similar structure with regards to lattice spacing. The most distinctive property specific to the polymerizing plus end was left-handed twisting in the inter-dimer interface, suggesting that the twisting might accelerate fast polymerization at the plus ends. Our analysis uncovered the heterogeneity of native microtubules and will be indispensable for the study of microtubules dynamics under physiological contexts or during specific cellular events.