This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplemental material
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Google Scholar
Right arrow Articles by Polka, J. K.
Right arrow Articles by Mullins, R. D.
PubMed
Right arrow PubMed Citation
Right arrow Articles by Polka, J. K.
Right arrow Articles by Mullins, R. D.

 Previous Article  |  Next Article 

Journal of Bacteriology, October 2009, p. 6219-6230, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00676-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Structure and Assembly Dynamics of Plasmid Actin AlfA Imply a Novel Mechanism of DNA Segregation{triangledown} ,{dagger}

Jessica K. Polka,1 Justin M. Kollman,2,3 David A. Agard,2,3 and R. Dyche Mullins1*

Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158,1 Department of Biochemistry and Biophysics, University of California, San Francisco, California 94518,2 The Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 941583

Received 23 May 2009/ Accepted 31 July 2009

Bacterial cytoskeletal proteins participate in a variety of processes, including cell division and DNA segregation. Polymerization of one plasmid-encoded, actin-like protein, ParM, segregates DNA by pushing two plasmids in opposite directions and forms the current paradigm for understanding active plasmid segregation. An essential feature of ParM assembly is its dynamically instability, the stochastic switching between growth and disassembly. It is unclear whether dynamic instability is an essential feature of all actin-like protein-based segregation mechanisms or whether bacterial filaments can segregate plasmids by different mechanisms. We expressed and purified AlfA, a plasmid-segregating actin-like protein from Bacillus subtilis, and found that it forms filaments with a unique structure and biochemistry; AlfA nucleates rapidly, polymerizes in the presence of ATP or GTP, and forms highly twisted, ribbon-like, helical filaments with a left-handed pitch and protomer nucleotide binding pockets rotated away from the filament axis. Intriguingly, AlfA filaments spontaneously associate to form uniformly sized, mixed-polarity bundles. Most surprisingly, our biochemical characterization revealed that AlfA does not display dynamic instability and is relatively stable in the presence of diphosphate nucleotides. These results (i) show that there is remarkable structural diversity among bacterial actin filaments and (ii) indicate that AlfA filaments partition DNA by a novel mechanism.

* Corresponding author. Mailing address: Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94158. Phone: (415) 502-4838. Fax: (415) 502-4838. E-mail: dyche{at}mullinslab.ucsf.edu

{triangledown} Published ahead of print on 7 August 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2009, p. 6219-6230, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00676-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»