title: Mass distribution and spatial organization of the linear bacterial motor of Spiroplasma citri R8A2.
abstract: In the simple, helical, wall-less bacterial genus Spiroplasma, chemotaxis and motility are effected by a linear, contractile motor arranged as a flat cytoskeletal ribbon attached to the inner side of the membrane along the shortest helical line. With scanning transmission electron microscopy and diffraction analysis, we determined the hierarchical and spatial organization of the cytoskeleton of Spiroplasma citri R8A2. The structural unit appears to be a fibril, approximately 5 nm wide, composed of dimers of a 59-kDa protein; each ribbon is assembled from seven fibril pairs. The functional unit of the intact ribbon is a pair of aligned fibrils, along which pairs of dimers form tetrameric ring-like repeats. On average, isolated and purified ribbons contain 14 fibrils or seven well-aligned fibril pairs, which are the same structures observed in the intact cell. Scanning transmission electron microscopy mass analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified cytoskeletons indicate that the 59-kDa protein is the only constituent of the ribbons.
authors.affiliation: Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel. shlomot@cc.huji.ac.il
authors.forename: Shlomo
authors.initials: S
authors.lastname: Trachtenberg
authors.forename: S Brian
authors.initials: SB
authors.lastname: Andrews
authors.forename: Richard D
authors.initials: RD
authors.lastname: Leapman
mesh_terms: D001426:Bacterial Proteins; D002633:Chemotaxis; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D003599:Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000648:ultrastructure*; D013149:Spiroplasma / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; D020409:Molecular Motor Proteins; C069778:fibril protein, Spiroplasma citri