Molecular assembly and mechanics of single vimentin intermediate filaments

Intermediate filaments (IF) are involved in key cellular functions including polarization, migration, and protection against large deformations. These functions are related to their remarkable ability to extend without breaking, a capacity that should be determined by the molecular organization of subunits within filaments. However, this structure-mechanics relationship remains poorly understood at the molecular level. I will present how, using super-resolution microscopy (SRM), we showed that vimentin filaments exhibit a ~49 nm axial repeat both in cells and in vitro. Using a SRM compatible stretching device, we also provided evidence that the extensibility of vimentin is due to the unfolding of its subunits and not to their sliding, thus establishing a direct link between the structural organization and its mechanical properties [1]. In a second part, I will show recent results on the in vitro reconstitution of vimentin assembly dynamics. We showed that vimentin filaments can spontaneously break without cofactors or post-translational modifications, but this fragmentation limits assembly only at very long-time scale (>18h) [2]. We also uncovered the mechanism responsible for fragmentation which involves subunit exchange. Our results show how vimentin filaments self-repair to protect their integrity and provide new insights into the physical understanding of the intermediate filament length regulation.

REFERENCES
[1] F. Nunes Vincente, M. Lelek, J.-Y. Tinevez, Q.D. Tran, G. Pehau-Arnaudet, C. Zimmer, S. Etienne-Manneville, G. Giannone, and C. Leduc, Molecular organization and mechanics of single vimentin filaments revealed by super-resolution imaging, Science Advances 8 (2022) eabm2696. doi: 10.1126/sciadv.abm2696.
[2] Q.D. Tran, V. Sorichetti, G. Pehau-Arnaudet, M. Lenz M+, and C. Leduc, Fragmentation and entanglement limit vimentin intermediate filament assembly, PRX 13 (2023) 011014 doi:10.1103/PhysRevX.13.011014.