Dynamics of the Bacterial Intermediate Filament Crescentin In Vitro and In Vivo

Background

Crescentin, the recently discovered bacterial intermediate filament protein,organizes into an extended filamentous structure that spans the length ofthe bacterium Caulobacter crescentus and plays a criticalrole in defining its curvature. The mechanism by which crescentin mediatescell curvature and whether crescentin filamentous structures are dynamicand/or polar are not fully understood.

Methodology/Principal Findings

Using light microscopy, electron microscopy and quantitative rheology, weinvestigated the mechanics and dynamics of crescentin structures. Live-cellmicroscopy reveals that crescentin forms structures in vivothat undergo slow remodeling. The exchange of subunits between thesestructures and a pool of unassembled subunits is slow during the life cycleof the cell however; in vitro assembly and gelation ofC. crescentus crescentin structures are rapid.Moreover, crescentin forms filamentous structures that are elastic,solid-like, and, like other intermediate filaments, can recover asignificant portion of their network elasticity after shear. The assemblyefficiency of crescentin is largely unaffected by monovalent cations(K⁺, Na⁺), but is enhanced bydivalent cations (Mg²⁺, Ca²⁺),suggesting that the assembly kinetics and micromechanics of crescentindepend on the valence of the ions present in solution.

Conclusions/Significance

These results indicate that crescentin forms filamentous structures that areelastic, labile, and stiff, and that their low dissociation rate fromestablished structures controls the slow remodeling of crescentin inC. crescentus.