Polymeric structures and dynamic properties of the bacterial actin AlfA

David Popp, Akihiro Narita, Umesh Ghoshdastider, Kayo Maeda, Yuichiro Maéda, Toshiro Oda, Tetsuro Fujisawa, Hirufumi Onishi, Kazuki Ito, Robert C. Robinson

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)


AlfA is a recently discovered DNA segregation protein from Bacillus subtilis that is distantly related to actin and the bacterial actin homologues ParM and MreB. Here we show that AlfA mostly forms helical 7/3 filaments, with a repeat of about 180Å, that are arranged in three-dimensional bundles. Other polymorphic structures in the form of two-dimensional rafts or paracrystalline nets were also observed. Here AlfA adopted a 16/7 helical symmetry, with a repeat of about 387Å. Thin polymers consisting of several intertwining filaments also formed. Observed helical symmetries of AlfA filaments differed from those of other members of the actin family: F-actin, ParM, or MreB. Both ATP and guanosine 5′-triphosphate are able to promote rapid AlfA filament formation with almost equal efficiencies. The helical structure is only preserved under physiological salt concentrations and at a pH between 6.4 and 7.4, the physiological range of the cytoplasm of B. subtilis. Polymerization kinetics are extremely rapid and compatible with a cooperative assembly mechanism requiring only two steps: monomer activation followed by elongation, making AlfA one of the most efficient polymerizing motors within the actin family. Phosphate release lags behind polymerization, and time-lapse total internal reflection fluorescence images of AlfA bundles are consistent with treadmilling rather than dynamic microtubule-like instability. High-pressure small angle X-ray scattering experiments reveal that the stability of AlfA filaments is intermediate between the stability of ParM and the stability of F-actin. These results emphasize that actin-like polymerizing machineries have diverged to produce a variety of filament geometries with diverse properties that are tailored for specific biological processes.

Original languageEnglish
Pages (from-to)1031-1041
Number of pages11
JournalJournal of Molecular Biology
Issue number4
Publication statusPublished - Apr 2010
Externally publishedYes


  • Actin homolog
  • AlfA
  • Electron microscopy
  • Helical symmetry
  • Treadmilling

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Molecular Biology


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