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  current news   Press   selected story    
     
  26th May 2010  
 

Filament Structure, Organization, and Dynamics in MreB Sheets

 
 




Author
David Popp1,2, Akihiro Narita13, Kayo Maeda1,3, Tetsuro Fujisawa4, Umesh Ghoshdastider3, Mitsusada Iwasa1, Yuichiro Mae´da1,3, and Robert C. Robinson2

1 ERATO “Actin Filament Dynamics” Project, Japan Science and Technology Corporation, c/o RIKEN Harima Institute, Japan

2 Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore

3 Structural Biology Research Center and Division of Biological Sciences, Nagoya University Graduate School of Science, Japan

4 Graduate School of Engineering, Department of Biomolecular Science, Gifu University, Japan

Abstract
In vivo fluorescence microscopy studies of bacterial cells have shown that the bacterial shape-determining protein and actin homolog, MreB, forms cable-like structures that spiral around the periphery of the cell. The molecular structure of these cables has yet to be established. Here we show by electron microscopy that Thermatoga maritime MreB forms complex, several µm long multilayered sheets consisting of diagonally interwoven filaments in the presence of either ATP or GTP. This architecture, in agreement with recent rheological measurements on MreB cables, may have superior mechanical properties and could be an important feature for maintaining bacterial cell shape. MreB polymers within the sheets appear to be single-stranded helical filaments rather than the linear protofilaments found in the MreB crystal structure. Sheet assembly occurs over a wide range of pH, ionic strength, and temperature. Polymerization kinetics are consistent with a cooperative assembly mechanism requiring only two steps: monomer activation followed by elongation. Steady-state TIRF microscopy studies of MreB suggest filament treadmilling while high pressure small angle x-ray scattering measurements indicate that the stability of MreB polymers is similar to that of F-actin filaments. In the presence of ADP or GDP, long, thin cables formed in which MreB was arranged in parallel as linear protofilaments. This suggests that the bacterial cell may exploit various nucleotides to generate different filament structures within cables for specific MreB-based functions.

 

 
 

 
 


Figure Legend:
Left: Typical electron micrograph of MreB cables, scale bar 200 nm. Right: Schematic illustration of the molecular structure within cables deduced from image analysis of electron micrographs.

Published, JBC Papers in Press, March 11, 2010, DOI 10.1074/jbc.M109.095901

For more information on Robert Robinson’s lab, please click here