Bacterial intermediate filaments: in vivo assembly, organization, and dynamics of crescentin

Abstract

Crescentin, which is the founding member of a rapidly growing family of bacterial cytoskeletal proteins, was previously proposed to resemble eukaryotic intermediate filament (IF) proteins based on structural prediction and in vitro polymerization properties. Here, we demonstrate that crescentin also shares in vivo properties of assembly and dynamics with IF proteins by forming stable filamentous structures that continuously incorporate subunits along their length and that grow in a nonpolar fashion. De novo assembly of crescentin is biphasic and involves a cell size-dependent mechanism that controls the length of the structure by favoring lateral insertion of crescentin subunits over bipolar longitudinal extension when the structure ends reach the cell poles. The crescentin structure is stably anchored to the cell envelope, and this cellular organization requires MreB function, identifying a new function for MreB and providing a parallel to the role of actin in IF assembly and organization in metazoan cells. Additionally, analysis of an MreB localization mutant suggests that cell wall insertion during cell elongation normally occurs along two helices of opposite handedness, each counterbalancing the other's torque.[Keywords: Crescentin; Caulobacter crescentus; intermediate filament; MreB; in vivo assembly; dynamics] Supplemental material is available at http://www.genesdev.org.

Three-dimensional superresolution colocalization of intracellular protein superstructures and the cell surface in live Caulobacter crescentus

“…2G and Movie S3). In agreement with previous diffraction-limited optical studies, the CreS fiber is often localized near the inner cell surface (33,34). In predivisional cells, the fiber extends across the division septum, as evidenced by the pinching membrane sensed by the Nile red dye.…”

Physics of Bacterial Morphogenesis

“…Indeed, most of the assembled cytoskeletal structures in bacterial cells appear to be dynamic: FtsZ in the Z ring dynamically exchanges with monomers in the cytoplasm (139). MreB filaments connected with the membrane also exchange monomers with the cytoplasm (41,136), although crescentin appears to be rather stable (28,57). Indeed, MreB was thought to be a helical bundle (158), but recent evidence from B. subtilis suggests that MreB proteins are short filaments that are dynamically transported in a cell wall assembly complex (47,64).…”

A novel coiled-coil repeat variant in a class of bacterial cytoskeletal proteins

“…Although a-helical coiled coils are ubiquitous in all kingdoms of life, true IF proteins have been found throughout metazoans but not conclusively in bacteria or plants. A few notable IF-like proteins, which exhibit many, but not all (Herrmann and Aebi, 2004), of the key IF features, have been demonstrated in bacteria, however: CfpA (You et al, 1996), CreS (Ausmees et al, 2003;Charbon et al, 2009), Scc (Mazouni et al, 2006), FilP (Bagchi et al, 2008). In plants there is some evidence of IF-like proteins from antigen cross-reactivity (e.g.…”