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Are ParM filaments polar or bipolar?
Vitold E Galkin1, Albina Orlova, Edward H Egelman
1Department of Biochemistry and Molecular Genetics, University of Virginia, Box 800733, Charlottesville, VA 22908-0733, USA.
Journal of Molecular Biology
|August 28, 2012
Summary
Bacterial actin homolog ParM filaments were analyzed for their structure. Existing data and helical diffraction analysis confirm ParM filaments are polar, not bipolar as suggested by Erickson.
Area of Science:
- Structural biology
- Microbiology
Background:
- Bacterial actin homolog ParM filaments are crucial for cell division.
- A recent perspective proposed ParM filaments may be bipolar, with antiparallel strands, challenging existing models.
Purpose of the Study:
- To investigate the structural polarity of bacterial actin homolog ParM filaments.
- To evaluate the validity of a proposed bipolar model for ParM filaments.
Main Methods:
- Analysis of existing electron cryo-microscopy and X-ray diffraction data.
- Application of helical diffraction principles to distinguish between polar and bipolar filament models.
- Processing of filament data under the assumption of a bipolar structure.
Main Results:
- Helical diffraction distinguishes polar from bipolar filaments based on asymmetric unit size.
- Existing structural data from electron cryo-microscopy and X-ray diffraction exclude a bipolar model for ParM.
- Processing data assuming a bipolar structure paradoxically resulted in the identification of polar filaments.
Conclusions:
- The proposed bipolar model for bacterial actin homolog ParM filaments is inconsistent with existing structural data.
- Analysis confirms that ParM filaments exhibit polar structure.
- The study reinforces the understanding of ParM filament organization in bacteria.
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