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The structure of bacterial ParM filaments

Nature Structural & Molecular Biology volume 14, pages 921–926 (2007)Cite this article

Abstract

Bacterial ParM is a homolog of eukaryotic actin and is involved in moving plasmids so that they segregate properly during cell division. Using cryo-EM and three-dimensional reconstruction, we show that ParM filaments have a different structure from F-actin, with very different subunit-subunit interfaces. These interfaces result in the helical handedness of the ParM filament being opposite to that of F-actin. Like F-actin, ParM filaments have a variable twist, and we show that this involves domain-domain rotations within the ParM subunit. The present results yield new insights into polymorphisms within F-actin, as well as the evolution of polymer families.

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Figure 1: Electron micrographs of ParM.
Figure 2: Variable twist, and overcoming it with the IHRSR approach.
Figure 3: Filaments of ParM have the opposite handedness to that of F-actin.
Figure 4: Domain rotations within ParM.
Figure 5: Absence of nucleotide exchange after ParM polymerization.

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Acknowledgements

This work was supported by US National Institutes of Health grants GM081303 (to E.H.E.) and GM061010 and GM675287 (to R.D.M.).

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Authors and Affiliations

  1. Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, 22908-0733, Virginia, USA

    Albina Orlova, Vitold E Galkin & Edward H Egelman

  2. Department of Cellular and Molecular Pharmacology, University of California San Francisco Medical School, San Francisco, 94107, California, USA

    Ethan C Garner & R Dyche Mullins

  3. Department of Cell Biology, Washington University School of Medicine, St. Louis, 63110, Missouri, USA

    John Heuser

Authors
  1. Albina Orlova
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  3. Vitold E Galkin
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  6. Edward H Egelman
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Contributions

A.O. prepared samples and did the EM; E.C.G. prepared samples; V.E.G. did image analysis; J.H. did the quick-freeze/deep-etch EM; R.D.M. did the nucleotide-exchange experiments; E.H.E. did image analysis.

Corresponding author

Correspondence to Edward H Egelman.

Supplementary information

Supplementary Video 1

Variable twist in ParM filaments. An animated GIF showing the averaged power spectra computed from the segments in five different bins of the histogram in Fig. 2a. This shows clearly that the sorting is effective, as the power spectra behave exactly as one would expect from segments having different twists. The layer lines shift positions (with respect to the distance from the equator) as the twist varies in these segments. (GIF 572 kb)

Supplementary Video 2

Domains rotate as twist changes. An animated GIF showing a comparison between two twist states of ParM filaments (165.2° and 169.6°) reconstructed from frozen-hydrated specimens (n ∼ 6,000 segments for each). The change in twist (∼ 4°) can be seen to be coupled with a larger change (∼ 10°) in the domain-domain orientation of the two major domains within the ParM subunit. (GIF 1270 kb)

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Orlova, A., Garner, E., Galkin, V. et al. The structure of bacterial ParM filaments. Nat Struct Mol Biol 14, 921–926 (2007). https://doi.org/10.1038/nsmb1300

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