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Molecular structure of the ParM polymer and the mechanism leading to its nucleotide-driven dynamic instability

David Popp1, Akihiro Narita, Toshiro Oda

  • 1ERATO Actin Filament Dynamics Project, RIKEN Harima Institute, Japan Science and Technology Corporation, Sayo, Hyogo, Japan. dpopp@spring8.or.jp

The EMBO Journal
|January 12, 2008
PubMed

Insights

ParM protein filaments, essential for bacterial plasmid segregation, are driven by GTP, not ATP. This GTP-driven mechanism allows ParM to act as a molecular switch, enabling dynamic filament assembly and disassembly for DNA segregation.

Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • ParM is a prokaryotic actin homologue crucial for plasmid segregation during bacterial cell division.
  • ParM filaments resemble eukaryotic microtubule spindles but their structural mechanism and dynamic instability are poorly understood.

Purpose of the Study:

  • To elucidate the structural mechanism and dynamic instability of ParM filaments during DNA segregation.
  • To determine the nucleotide dependency and conformational changes underlying ParM filament function.

Main Methods:

  • Biochemical assays
  • Total Internal Reflection Fluorescence (TIRF) microscopy
  • High-pressure Small-Angle X-ray (SAX) scattering
  • Electron microscopy image analysis
  • X-ray fiber diffraction

Main Results:

  • ParM filament polymerization and disintegration are GTP-dependent, functioning as a GTP-driven molecular switch.
  • ParM filaments form a left-handed helix, distinct from actin's right-handed helix, yet share similar intersubunit contacts.
  • An atomic model of the ParM-GMPPNP filament explains filament disintegration upon nucleotide release due to conformational changes.

Conclusions:

  • ParM utilizes a GTP-driven mechanism for dynamic filament assembly and disassembly, crucial for its role in plasmid segregation.
  • The structural differences and nucleotide-driven conformational changes of ParM are key to its function as a molecular switch in prokaryotic DNA segregation.

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