title: Bacillus anthracis tubulin-related protein Ba-TubZ assembles force-generating polymers.
abstract: Pathogenicity of Bacillus anthracis depends on the faithful inheritance of plasmid pXO1, in a process that requires the plasmid encoded tubulin-related protein Ba-TubZ. Here we show, using heterologous expression in Schizosaccharomyces pombe, that Ba-TubZ assembles into a dynamic polymer in the absence of other B. anthracis proteins and can generate force capable of deforming the fission yeast nuclear envelope. The polymer bundles contain 27 ± 15 protofilaments/μm assuming that each protofilament spans the entire length. Thinner appearing buckled and thicker appearing straight filaments of Ba-TubZ were both capable of inducing nuclear envelope deformation. Unlike the related protein Bt-TubZ from Bacillus thuringiensis, which undergoes treadmilling upon expression in fission yeast, Ba-TubZ polymers did not undergo detectable treadmilling. Instead, in fluorescence recovery after photobleaching experiments, it displayed a different turnover behavior characterized by moderate fluorescence recovery along the entire length of the polymer. Modeling Ba-TubZ bundles as Euler-Bernoulli beams that buckle under compressive loads when pushed against the nuclear envelope allowed us to estimate that Ba-TubZ generates forces in the order of 1-10 nN. We propose that polymerization based filament elongation and force generation might aid faithful segregation of the virulence plasmid.
authors.affiliation: Mechanobiology Institute, The National University of Singapore.
authors.forename: Ramanujam
authors.initials: R
authors.lastname: Srinivasan
authors.forename: Mithilesh
authors.initials: M
authors.lastname: Mishra
authors.forename: Fong Yew
authors.initials: FY
authors.lastname: Leong
authors.forename: Keng-Hwee
authors.initials: KH
authors.lastname: Chiam
authors.forename: Mohan
authors.initials: M
authors.lastname: Balasubramanian
mesh_terms: D001408:Bacillus anthracis / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D001413:Bacillus thuringiensis / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D009685:Nuclear Envelope / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization / Q000502:physiology*; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins