title: Tubulin-like protofilaments in Ca2+-induced FtsZ sheets.
abstract: The 40 kDa protein FtsZ is a major septum-forming component of bacterial cell division. Early during cytokinesis at midcell, FtsZ forms a cytokinetic ring that constricts as septation progresses. FtsZ has a high propensity to polymerize in vitro into various structures, including sheets and filaments, in a GTP-dependent manner. Together with limited sequence homology, the occurrence of the tubulin signature motif in FtsZ and a similar three-dimensional structure, this leads to the conclusion that FtsZ is the bacterial tubulin homologue. We have polymerized FtsZ1 from Methanococcus jannaschii in the presence of millimolar concentrations of Ca2+ ions to produce two-dimensional crystals of plane group P2221. Most of the protein precipitates and forms filaments approximately 23.0 nm in diameter. A three-dimensional reconstruction of tilted micrographs of FtsZ sheets in negative stain between 0 and 60 degrees shows protofilaments of FtsZ running along the sheet axis. Pairs of parallel FtsZ protofilaments associate in an antiparallel fashion to form a two-dimensional sheet. The antiparallel arrangement is believed to generate flat sheets instead of the curved filaments seen in other FtsZ polymers. Together with the subunit spacing along the protofilament axis, a fitting of the FtsZ crystal structure into the reconstruction suggests a protofilamant structure very similar to that of tubulin protofilaments.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.jyl@mrc-lmb.cam.ac.uk
authors.forename: J
authors.initials: J
authors.lastname: Löwe
authors.forename: L A
authors.initials: LA
authors.lastname: Amos
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000378:metabolism / Q000648:ultrastructure*; D002118:Calcium / Q000494:pharmacology*; D002455:Cell Division; D020558:GTP Phosphohydrolases / Q000378:metabolism / Q000648:ultrastructure; D007091:Image Processing, Computer-Assisted; D017017:Methanococcus; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D014404:Tubulin / Q000648:ultrastructure
chemical_list: D019843:Archaeal Proteins; C119586:FtsZ protein, Methanococcus jannaschii; D014404:Tubulin; D020558:GTP Phosphohydrolases; D002118:Calcium