title: GTP-dependent polymerization of the tubulin-like RepX replication protein encoded by the pXO1 plasmid of Bacillus anthracis.
abstract: RepX protein encoded by the pXO1 plasmid of Bacillus anthracis is required for plasmid replication. RepX harbours the tubulin signature motif and contains limited amino acid sequence homology to the bacterial cell division protein FtsZ. Although replication proteins are not known to polymerize, here we show by electron microscopy that RepX undergoes GTP-dependent polymerization into long filaments. RepX filaments assembled in the presence of GTPgammaS were more stable than those assembled in the presence of GTP, suggesting a role for GTP hydrolysis in the depolymerization of the filaments. Light scattering studies showed that RepX underwent rapid polymerization, and substitution of GTP with GTPgammaS stabilized the filaments. RepX exhibited GTPase activity and a mutation in the tubulin signature motif severely impaired its GTPase activity and its polymerization in vitro. Unlike FtsZ homologues, RepX harbours a highly basic carboxyl-terminal region and exhibits GTP-dependent, non-specific DNA binding activity. We speculate that RepX may be involved in both the replication and segregation of the pXO1 plasmid.
authors.affiliation: Department of Microbiology and Molecular Genetics, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Syam P
authors.initials: SP
authors.lastname: Anand
authors.forename: Parvez
authors.initials: P
authors.lastname: Akhtar
authors.forename: Eowyn
authors.initials: E
authors.lastname: Tinsley
authors.forename: Simon C
authors.initials: SC
authors.lastname: Watkins
authors.forename: Saleem A
authors.initials: SA
authors.lastname: Khan
mesh_terms: D001408:Bacillus anthracis / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001704:Biopolymers; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D006160:Guanosine Triphosphate / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001704:Biopolymers; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; C071525:FtsZ protein, Bacteria; D014404:Tubulin; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases