A bacterial linear motor: cellular and molecular organization of the contractile cytoskeleton of the helical bacterium <i>Spiroplasma melliferum</i> BC3

Trachtenberg, Shlomo; Gilad, Rami

doi:10.1046/j.1365-2958.2001.02527.x

Cited by 83 publications

(156 citation statements)

References 65 publications

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“…4A) and a membrane-bound, cytoskeleton-like ribbon, which follows the inner, shortest helical path of the cell (Fig. 4B) (163). The cytoskeleton from Spiroplasma was isolated a long time ago, and it was thought to consist of a single protein, the 55-kDa fibril protein, currently exclusive to Spiroplasma (162).…”

Section: Mreb Proteins and Cell Shape Determination In Wall-less Prokmentioning

confidence: 99%

The Bacterial Actin-Like Cytoskeleton

Carballido-López

2006

Microbiol Mol Biol Rev

177

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SUMMARY Recent advances have shown conclusively that bacterial cells possess distant but true homologues of actin (MreB, ParM, and the recently uncovered MamK protein). Despite weak amino acid sequence similarity, MreB and ParM exhibit high structural homology to actin. Just like F-actin in eukaryotes, MreB and ParM assemble into highly dynamic filamentous structures in vivo and in vitro. MreB-like proteins are essential for cell viability and have been implicated in major cellular processes, including cell morphogenesis, chromosome segregation, and cell polarity. ParM (a plasmid-encoded actin homologue) is responsible for driving plasmid-DNA partitioning. The dynamic prokaryotic actin-like cytoskeleton is thought to serve as a central organizer for the targeting and accurate positioning of proteins and nucleoprotein complexes, thereby (and by analogy to the eukaryotic cytoskeleton) spatially and temporally controlling macromolecular trafficking in bacterial cells. In this paper, the general properties and known functions of the actin orthologues in bacteria are reviewed.

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Section: Mreb Proteins and Cell Shape Determination In Wall-less Prokmentioning

confidence: 99%

The Bacterial Actin-Like Cytoskeleton

Carballido-López

2006

Microbiol Mol Biol Rev

177

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“…To this point, data analysis has been based on diffraction patterns of images of ribbons and bundles in which all structural features are averaged, but the cytoskeletal ribbons are linear motors whose subunit spacing is expected to vary during contraction and expansion (21,22). Whereas the average distances between subunits are determined by the spatial frequencies of the diffraction spots, the variation in subunit spacing can be determined directly from images.…”

Section: Resultsmentioning

confidence: 99%

“…Both tube and cytoskeleton are mutually coiled into a dynamic helix, the latter driving the former. The cytoskeletal ribbon functions as a linear motor by differentially changing the length of its fibril components (21).…”

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confidence: 99%

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Mass Distribution and Spatial Organization of the Linear Bacterial Motor ofSpiroplasma citriR8A2

2003

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In the simple, helical, wall-less bacterial genus Spiroplasma, chemotaxis and motility are effected by a linear, contractile motor arranged as a flat cytoskeletal ribbon attached to the inner side of the membrane along the shortest helical line. With scanning transmission electron microscopy and diffraction analysis, we determined the hierarchical and spatial organization of the cytoskeleton of Spiroplasma citri R8A2. The structural unit appears to be a fibril, ϳ5 nm wide, composed of dimers of a 59-kDa protein; each ribbon is assembled from seven fibril pairs. The functional unit of the intact ribbon is a pair of aligned fibrils, along which pairs of dimers form tetrameric ring-like repeats. On average, isolated and purified ribbons contain 14 fibrils or seven well-aligned fibril pairs, which are the same structures observed in the intact cell. Scanning transmission electron microscopy mass analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified cytoskeletons indicate that the 59-kDa protein is the only constituent of the ribbons.The mollicutes (Spiroplasma, Mycoplasma, and Acholeplasma spp.) are the smallest and simplest free-living and selfreplicating forms of life. The mollicutes evolved by regressive evolution and genome reduction from the genus Clostridium (for a review, see reference 15). The reduced genome of the mollicutes yields a minimal inventory of cellular components and extreme structural simplicity. Nonetheless, the cells have a well-defined shape, are chemotactic and motile, and demonstrate a variety of cell movements and dynamic morphologies. For example, mycoplasmas and acholeplasmas glide on solid and semisolid surfaces, while the spiroplasmas (2) are free swimmers (for a review, see reference 11).The mollicutes lack cell walls and flagella but have an internal, contractile cytoskeleton that functions as a linear motor (for a review, see reference 20). The spiroplasmas have a particularly unique cellular geometry, such that the Spiroplasma cell can be viewed as a membranous tube to which a flat cytoskeletal ribbon of parallel fibrils is attached along the shortest helical line on the inner surface of the cellular tube. Both tube and cytoskeleton are mutually coiled into a dynamic helix, the latter driving the former. The cytoskeletal ribbon functions as a linear motor by differentially changing the length of its fibril components (21).The genus Spiroplasma was first described by Saglio et al. (16). Williamson (25) and Williamson and Whitcomb (26) reported the isolation of Spiroplasma cytoskeletons by cell lysis and detergent extraction. It has also been shown that cytoskeletons can be released from Spiroplasma cells by repeated freezing and thawing (19). Further electron microscopy studies on Spiroplasma spp. (4,5,17,27) led to a model of a flat, polar, dense cytoskeletal ribbon ϳ94 nm wide attached to the inner surface of the cell membrane and constructed from ϳ4.5-to 5.0-nm-diameter fibrils with an ϳ9-nm repeat. The cytoskeleton accounts for ϳ1% of the total cell...

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“…Arrays of longitudinally oriented fibrillar structures have been observed by electron microscopy of intact and disrupted cells of S. melliferum (208)(209)(210). The structures contain a 55-to 59-kDa protein that has not been further identified.…”

Section: Other Filamentous Intracellular Structuresmentioning

confidence: 99%

The Bacterial Cytoskeleton

Shih

Rothfield

2006

Microbiol Mol Biol Rev

243

220

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SUMMARY In recent years it has been shown that bacteria contain a number of cytoskeletal structures. The bacterial cytoplasmic elements include homologs of the three major types of eukaryotic cytoskeletal proteins (actin, tubulin, and intermediate filament proteins) and a fourth group, the MinD-ParA group, that appears to be unique to bacteria. The cytoskeletal structures play important roles in cell division, cell polarity, cell shape regulation, plasmid partition, and other functions. The proteins self-assemble into filamentous structures in vitro and form intracellular ordered structures in vivo. In addition, there are a number of filamentous bacterial elements that may turn out to be cytoskeletal in nature. This review attempts to summarize and integrate the in vivo and in vitro aspects of these systems and to evaluate the probable future directions of this active research field.

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A bacterial linear motor: cellular and molecular organization of the contractile cytoskeleton of the helical bacterium Spiroplasma melliferum BC3

Cited by 83 publications

References 65 publications

The Bacterial Actin-Like Cytoskeleton

The Bacterial Actin-Like Cytoskeleton

Mass Distribution and Spatial Organization of the Linear Bacterial Motor ofSpiroplasma citriR8A2

The Bacterial Cytoskeleton

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