Are ParM filaments polar or bipolar?

J Mol Biol. 2012 Nov 2;423(4):482-5. doi: 10.1016/j.jmb.2012.08.006. Epub 2012 Aug 21.


A recent perspective [Erickson, H. (2012). Bacterial actin homolog ParM: arguments for an apolar, antiparallel double helix. J. Mol. Biol., 422, 461-463] by Harold Erickson has suggested that published reconstructions of bacterial ParM filaments from three different laboratories may have artifactually imposed polarity upon a filament that is really bipolar, with the two strands running in opposite directions. We show that Erickson's model of a bipolar filament can be easily distinguished from a polar filament by helical diffraction, since the asymmetric unit in a bipolar filament would be twice the size as that in a polar filament. Existing data from both electron cryo-microscopy and X-ray diffraction exclude a bipolar model. We adopt the suggestion put forward by Erickson to process filaments, assuming that they are bipolar, and show that the resulting filaments are polar.

Publication types

  • Research Support, N.I.H., Extramural
  • Comment

MeSH terms

  • Actin Cytoskeleton / chemistry*
  • Actins / chemistry*
  • Escherichia coli Proteins / chemistry*


  • Actins
  • Escherichia coli Proteins