Tsai, C.-N. G.; Le Blanc, L.; Elgebely, F. M. F.; Al-Mayyah, Z.; Nilges, M.; Persat, A.; Karami, Y.

Biological machines operate under mechanical load, requiring architectures that simultaneously resist force and remain functionally dynamic. Type IV pili (T4P) are bacterial filaments that experience large tensile forces during motor-driven retraction. Here, we combine cryo-electron microscopy, molecular dynamics simulations, optical tweezers, and functional analyses to define the structural basis of T4P mechanical adaptation. We determined a 2.8 [A] cryo-EM structure of the Pseudomonas aeruginosa T4P and integrated it with comparative all-atom simulations across six bacterial strains to identify a conserved force-bearing electrostatic network. Simulations predicted that this network tunes filament elasticity under load, a finding validated by single-filament force spectroscopy. Rewiring these interactions experimentally produced hyper-rigid pili that assembled normally but exhibited impaired twitching motility. Together, our findings uncover a structural trade-off between force-resistant architecture and reversible supramolecular adaptability.