Zooming into the Cytoskeleton: Nanodefect-Initiated Microtubule Catastrophe Filmed by High-Speed Atomic Force Microscopy

Microtubule catastrophe is widely attributed to an end-driven loss of the GTP cap, implying that structural failure is confined to filament termini. Here, we show that this view is incomplete. Using high-speed atomic force microscopy (HS-AFM), we directly visualize nanoscale structural failure in paclitaxel-treated microtubules in real time. We identify spontaneous lattice nanodefects that emerge within the filament shaft and act as internal initiation sites for disassembly. These defects arise from localized protofilament decoupling and lattice strain accumulation, which disrupt the cooperative interactions within the microtubule wall. Once a critical threshold is reached, these sites nucleate disassembly that propagates as distinct collapse trajectories, including bidirectional spreading from intralattice defects and inward convergence from opposing ends, in addition to classical end-initiated depolymerization. Rather than uniformly stabilizing the lattice, paclitaxel maintains microtubules in a metastable state in which internal stress heterogeneity persists and enables defect-driven failure. Our results establish lattice decoupling as a primary structural trigger of microtubule catastrophe and redefine it as a defect-mediated, spatially encoded transition. These findings provide a nanoscale mechanistic framework for understanding heterogeneous responses to microtubule-targeting chemotherapeutics, suggesting that drug resistance may arise from modulation of lattice integrity and defect propagation rather than drug binding alone.