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  current news   Press   selected story    
     
  7th September 2012  
  Microtubule-like properties of the bacterial actin homolog ParM-R1
 
 




Authors
David Popp1, Akihiro Narita2, Lin Jie Lee1, Mårten Larsson1, Robert C. Robinson1,3,4

1 -
Institute of Molecular and Cell Biology, Proteos, 61 Biopolis Drive, Singapore, 138673.
2 -
Nagoya University Graduate School of Science, Structural Biology Research Center and Division of Biological Sciences, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan.
3 -
Department of Biochemistry, National University of Singapore, 8 Medical Drive, Singapore 117597.
4 -
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore, 637551.

Published online in Journal of Biological Chemistry on August 20, 2012

Abstract

In preparation for mammalian cell division, microtubules repeatedly probe the cytoplasm in order to capture chromosomes and assemble the mitotic spindle. Critical features of this microtubule system are the formation of radial arrays centered at the centrosomes and dynamic instability, leading to persistent cycles of polymerization and depolymerization. Here, we show that the actin homolog, ParM-R1 that drives segregation of the R1 multidrug resistance plasmid from E. coli can also self-organize in vitro into asters, which resemble astral microtubules. ParM-R1 asters grow from centrosome-like structures consisting of interconnected nodes related by a pseudo eight-fold symmetry. In addition we show that ParM-R1 is able to perform persistent microtubule-like oscillations of assembly and disassembly. In vitro, a whole population of ParM-R1 filaments is synchronized between phases of growth and shrinkage, leading to prolonged synchronous oscillations even at physiological ParM-R1 concentrations. These results imply that the selection pressure to reliably segregate DNA during cell division has led to common mechanisms within diverse segregation machineries.


Figure Legend:
(A) ParM asters grow from an initial nucleus of interconnected nodes related by a pseudo 8-fold symmetry. Scale bar 100 nm. (B) Fully developed asters. Scale bar 1µm. (C) Microtubule-like periodic oscillations of ParM detected by light scattering. (D) Model of the reaction cycle responsible for oscillations. ParM-R1 monomers (green conformation) are activated by addition of GTP (yellow conformation) (1) and assemble via a nucleation step (2) into filaments (3). GTP to GDP is hydrolyzed upon polymerization forming a GTP-ParM-R1 capped filament (3). GDP dissociation leads to disassembly of ParM-R1 filaments into oligomers (4). These oligomers transiently lock the subunits in a non-polymerized state, which when dissociate into monomers (5) can be recharged with GTP (1), leading to a regrowth of existing ParM-R1 filaments and/or new nucleation.



For more information on Robert ROBINSON's laboratory, please click here.