Continuous self-repair protects vimentin intermediate filaments from fragmentation

Area of Science:

• Cell biology
• Biophysics
• Cytoskeletal dynamics

Background:

• Intermediate filaments, like vimentin, regulate cell mechanics and migration.
• Vimentin forms a dynamic cytoplasmic network through remodeling processes.
• Filament elongation occurs via annealing, but shortening mechanisms like fragmentation are poorly understood.

Purpose of the Study:

• To elucidate the molecular mechanism of vimentin filament breakage.
• To understand the role of subunit exchange in filament dynamics and integrity.
• To investigate the self-repair mechanisms of vimentin filaments.

Main Methods:

• In vitro reconstitution of vimentin filaments.
• Fluorescence imaging and atomic force microscopy.
• Theoretical modeling and computational analysis.

Main Results:

• Vimentin filaments consist of exchangeable and immobile subunits, with exchangeable subunits forming tetramers.
• A continuous self-repair mechanism relies on soluble vimentin tetramers in equilibrium with filaments.
• Filament breakage is triggered by local fluctuations in tetramer number per cross-section due to subunit exchange.
• Approximately four tetramer removals from a cross-section lead to filament breakage.
• Binding energy analysis revealed differences between complete and disassembled filaments.

Conclusions:

• Subunit exchange dynamics directly link to vimentin filament fragmentation.
• Soluble vimentin tetramers are essential for maintaining filament integrity and self-repair.
• Understanding vimentin fragmentation provides insights into cytoskeletal regulation and cell mechanics.