title: Structural effects of mutations in Salmonella typhimurium flagellar switch complex.
abstract: Mutations in Salmonella typhimurium fliG, fliM and fliN give rise either to non-flagellate, non-motile or non-chemotactic mutant bacteria. The FliG, FliM and FliN proteins form part of recently characterized extended flagellar basal structures, and have been postulated to form a mutually interacting structural complex. We have examined basal body preparations from non-motile or non-chemotactic fliG, fliM and fliN mutant strains by electron microscopy and immunoblot gel analysis. Most flagellar preparations isolated from the non-motile mutants lacked FliM, but contained FliG. The basal bodies lacked the belled morphology characteristic of the wild-type structures, but had protrusions which could be labelled with anti-FliG. Non-motile mutant preparations severely depleted of FliG but containing FliM were also obtained. These preparations contained extended, belled flagellar structures that were labelled with anti-FliM. Thus, FliM is part of the shell of the extended structures responsible for the belled morphology, while FliG may be part of the inner substructure. The extended basal structures from a FliG temperature-sensitive mutant strain rapidly lost FliM, as well as FliG, upon a shift to a non-permissive temperature, implying interaction between the FliG- and FliM-containing substructures. In dramatic contrast to non-motile mutants, extended basal structures isolated from non-chemotactic mutants were indistinguishable from wild-type structures. This difference may reflect the energetics of the different protein-protein interactions operative during torque generation and the switching of rotation sense.
authors.affiliation: Department of Physiology & Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: R
authors.initials: R
authors.lastname: Zhao
authors.forename: S C
authors.initials: SC
authors.lastname: Schuster
authors.forename: S
authors.initials: S
authors.lastname: Khan
mesh_terms: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins / Q000032:analysis* / Q000235:genetics / Q000276:immunology; D002633:Chemotaxis / Q000235:genetics; D005407:Flagella / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure*; D005798:Genes, Bacterial / Q000235:genetics; D016253:Microscopy, Immunoelectron; D009154:Mutation; D012486:Salmonella typhimurium / Q000235:genetics / Q000276:immunology / Q000648:ultrastructure*; D013696:Temperature
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; C077389:FliN protein, Bacteria; C075660:Flig protein, Bacteria; C035832:hook protein, bacterial flagellum; C066821:FliM protein, Bacteria