RESEARCH HIGHLIGHTS

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CYTOSKELETON Remodelling the FtsZ network

In , the -related GTPase FtsZ of FtsZ that binds autonomously to the (filamentation temperatur­e-sensitive Z) membrane also formed a network of filament and -related FtsA are two components of bundles on the membrane; however, the Z-ring, a cytoskeletal structure that induces these bundles were stationary. Moreover, FtsZ . Although initial models for Z-ring filaments recruited to the membrane by the formation suggested that FtsA is a passive alternative membrane-anchor ZipA membrane anchor, recent data indicate that it (Z interacting protein) also assembled into a influences the organization of FtsZ filaments into stationary network, which suggests that the large-scale, dynamic cytoskeletal structures. interaction of FtsZ and FtsA is required for rapid Here, Loose and Mitchison investigate Z-ring and dynamic FtsZ filament reorganization. formation in vitro and uncover a dual role So, how does this rapid reorganization of the for FtsA in FtsZ network assembly and FtsZ filament network come about? The authors rearrangement: it first recruits FtsZ filaments to further studied the interaction of FtsA with FtsZ the membrane, and then negatively regulates and found that FtsA only recruits FtsZ filaments FtsZ organization. to the membrane but not FtsZ monomers. The authors used fluorescently labelled Moreover, they found that, in contrast to ZipA, FtsZ and FtsA , and reconstituted FtsZ FtsA destabilizes the FtsZ network. The polymerization on supported bilayers in vitro. underlying mechanism for this remains to be They found that, in the presence of FtsA, determined, but the authors suggest that GTP (which induces FtsZ polymerization) and fragmentation of FtsZ polymers leads to their ATP (which is required for FtsA–FtsZ interaction), detachment from the membrane, as short FtsZ FtsZ filaments attached to the membrane. At low fragments bind only weakly to FtsA, and this protein concentrations, the authors observed allows rapid reorganization of the FtsZ filament individual, short filaments, which grew at one network into dynamic structures. end and shortened at the opposite end — that Thus, remodelling of the FtsZ network into is, they showed behaviour, dynamic higher-order structures depends on similar to actin filaments. At higher protein FtsA, and the early stages of Z-ring formation concentrations, FtsZ filaments formed dynamic require the coordinated action of many factors. filament bundles that self-organized into chirally It will be interesting to see whether the rotating rings. Although the FtsZ filament mechanism of crosstalk between cytoskeletal network was continuously remodelling itself and regulators has common features with that in seemed to be moving, the authors found that other systems. single subunits remained static, which supports Andrea Du Toit the idea that remodelling of the filament This article originally appeared in Nature Rev. Microbiology (http://dx.doi.org/10.1038/nrmicro3196). network is driven by polymerization dynamics. Next, the authors asked whether these ORIGINAL RESEARCH PAPER Loose, M. & Mitchison, T. J. The observed dynamics are an intrinsic feature of bacterial proteins FtsA and FtsZ self-organize into FtsZ or whether they emerge from a complex dynamic cytoskeletal patterns. Nature Cell Biol. http://dx.doi. inter­action with FtsA. They show that a version org/10.1038/ncb2885 (2013)

NATURE REVIEWS | MOLECULAR CELL VOLUME 15 | JANUARY 2014

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