Filament structure, organization, and dynamics in MreB sheets.
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 mum 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.
Popp
David
D
ERATO Actin Filament Dynamics Project, Japan Science and Technology Corporation, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
Narita
Akihiro
A
Maeda
Kayo
K
Fujisawa
Tetsuro
T
Ghoshdastider
Umesh
U
Iwasa
Mitsusada
M
Maéda
Yuichiro
Y
Robinson
Robert C
RC
D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D055503:Protein Multimerization / Q000502:physiology*; D020836:Protein Structure, Quaternary; D020124:Thermotoga maritima / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C435905:MreB1 protein, Thermotoga maritima; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate