Dynamics of Vimentin intermediate filament enabled by the unique molecular nature of the protein

Mammalian cells are structured by an interpenetrating network with three major components: actin filaments, microtubules, and intermediate filaments. The intermediate filament is a family comprising tens of different members, among which vimentin is one of the most prevalent in humans and extensively studied. Here, we report a set of experiments to show that vimentin in live cells is a highly dynamic network with constant subunit exchange and network reconfiguration. The observed dynamics of vimentin contrast drastically with microtubules or actin filaments: the subunits can exchange between the filamentous and the dispersed or along the filament anywhere on the filament. The filament network constantly break-and-reform and undergoes topological change. Such dynamics also heavily depend on the phosphorylation level of the vimentin.

We propose that such unique dynamics of the filament are enabled by the molecular nature of the vimentin. The N-domain intrinsically disordered domains (IDRs) of vimentin aggregate in the middle of the filament and form a fluidic core, where the ordered domain of the molecule points outside and forms the wall of the filament. Such a structure resembles the structure of the amphiphilic molecules and the worm-like micelles. Therefore, the vimentin network is a self-assembled micelle rather than a polymer network. The phosphorylation level of the IDRs mediates the glass-to-liquid transition of the core and consequently enables the dynamics of the vimentin network.