Filament structure of bacterial tubulin homologue TubZ.
Low copy number plasmids often depend on accurate partitioning systems for their continued survival. Generally, such systems consist of a centromere-like region of DNA, a DNA-binding adaptor, and a polymerizing cytomotive filament. Together these components drive newly replicated plasmids to opposite ends of the dividing cell. The Bacillus thuringiensis plasmid pBToxis relies on a filament of the tubulin/FtsZ-like protein TubZ for its segregation. By combining crystallography and electron microscopy, we have determined the structure of this filament. We explain how GTP hydrolysis weakens the subunit-subunit contact and also shed light on the partitioning of the plasmid-adaptor complex. The double helical superstructure of TubZ filaments is unusual for tubulin-like proteins. Filaments of ParM, the actin-like partitioning protein, are also double helical. We suggest that convergent evolution shapes these different types of cytomotive filaments toward a general mechanism for plasmid separation.
Aylett
Christopher H S
CH
Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
Wang
Qing
Q
Michie
Katharine A
KA
Amos
Linda A
LA
Löwe
Jan
J
D001413:Bacillus thuringiensis / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000648:ultrastructure; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000648:ultrastructure; D003599:Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure; D004926:Escherichia coli / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D010710:Phosphates / Q000378:metabolism; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D015203:Reproducibility of Results; D017386:Sequence Homology, Amino Acid; D014404:Tubulin / Q000737:chemistry* / Q000648:ultrastructure
D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria; D010710:Phosphates; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D014404:Tubulin; D008274:Magnesium