An atlas of microtubule lattice parameters regulated through ligand binding to the microtubule stabilizing sites

Microtubules (MTs) are essential cytoskeletal polymers with dual functions: they generate mechanical forces necessary for processes such as mitosis and angiogenesis, and serve as static tracks for intracellular transport by motor proteins. Force generation is mediated by the cytomotive switch, a dynamic property modulated by MT stability. Second-generation microtubule-targeting agents (MTAs), such as paclitaxel and docetaxel, bind at the taxane site and chemically stabilize MTs by enhancing lateral and longitudinal tubulin interactions. While effective in blocking MT depolymerization and preserving transport, the fact that these drugs introduce structural alterations that distinguish stabilized MTs from their native counterparts raises concerns for both mechanistic studies and clinical applications in diseases like tauopathies.

In this study, we provide a detailed structural atlas of taxane site-mediated modulation of MTs. We show that drug binding induces two distinct lattice conformations in the longitudinal axis—expanded (4.17 nm rise) and compressed (4.06 nm rise)—with rapid transitions and low energy barriers between them. In contrast, lateral interactions allow multiple protofilament (PF) configurations with small energetic differences but high activation barriers, a finding consistent with the observed structural heterogeneity of MTs. Notably, minor chemical modifications, such as acetylation of paclitaxel’s C-7 hydroxyl, can shift these conformational equilibria. These structural changes significantly impact biochemical properties, and alter recognition by tau and kinesin proteins, suggesting a role for lattice conformation as a signaling cue. Our findings underscore the nuanced structural consequences of taxane-site ligand binding and its relevance in both therapeutic and experimental contexts.