Dynamic and asymmetric fluctuations in the microtubule wall captured by high-resolution cryoelectron microscopy

Significance The dynamic behavior of microtubules, a tubular polymer, is essential for numerous processes throughout the cell. Cryoelectron microscopy (cryo-EM) has provided high-resolution snapshots of the microtubule during its GTP hydrolysis cycle, which regulates assembly and depolymerization. However, the dynamic structural properties of microtubules remain less well understood, due to limitations in cryo-EM analysis methods. Here we present a method to subdivide the microtubule wall into elemental components during cryo-EM refinement. This method substantially enhances the quality of 3D cryo-EM reconstructions, and reveals stochastic fluctuations in the geometry of the microtubule wall. Distinct microtubule subpopulations were identified that exhibit large and systematic deviations from helical symmetry, with potential implications for microtubule assembly/disassembly and other dynamic behaviors that remains incompletely understood.