title: Treadmilling of a prokaryotic tubulin-like protein, TubZ, required for plasmid stability in Bacillus thuringiensis.
abstract: Prokaryotes rely on a distant tubulin homolog, FtsZ, for assembling the cytokinetic ring essential for cell division, but are otherwise generally thought to lack tubulin-like polymers that participate in processes such as DNA segregation. Here we characterize a protein (TubZ) from the Bacillus thuringiensis virulence plasmid pBtoxis, which is a member of the tubulin/FtsZ GTPase superfamily but is only distantly related to both FtsZ and tubulin. TubZ assembles dynamic, linear polymers that exhibit directional polymerization with plus and minus ends, movement by treadmilling, and a critical concentration for assembly. A point mutation (D269A) that alters a highly conserved catalytic residue within the T7 loop completely eliminates treadmilling and allows the formation of stable polymers at a much lower protein concentration than the wild-type protein. When expressed in trans, TubZ(D269A) coassembles with wild-type TubZ and significantly reduces the stability of pBtoxis, demonstrating a direct correlation between TubZ dynamics and plasmid maintenance. The tubZ gene is in an operon with tubR, which encodes a putative DNA-binding protein that regulates TubZ levels. Our results suggest that TubZ is representative of a novel class of prokaryotic cytoskeletal proteins important for plasmid stability that diverged long ago from the ancient tubulin/FtsZ ancestor.
authors.affiliation: Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Larsen
authors.forename: Christina
authors.initials: C
authors.lastname: Cusumano
authors.forename: Akina
authors.initials: A
authors.lastname: Fujioka
authors.forename: Grace
authors.initials: G
authors.lastname: Lim-Fong
authors.forename: Paula
authors.initials: P
authors.lastname: Patterson
authors.forename: Joe
authors.initials: J
authors.lastname: Pogliano
mesh_terms: D000595:Amino Acid Sequence; D001413:Bacillus thuringiensis / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010957:Plasmids / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014404:Tubulin / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria; D014404:Tubulin