title: Interactions of FliJ with the Salmonella type III flagellar export apparatus.
abstract: FliJ, a 17-kDa protein, is a soluble component of the Salmonella type III flagellar protein export system that has antiaggregation properties and several other characteristics that suggest it may have a chaperone-like function. We have now examined this protein in detail. Ten-amino-acid scanning deletions covering the entire 147-amino-acid sequence were tested for complementation of a fliJ null strain; only the first and last deletions complemented. A few of the deletions, especially towards the C terminus, exerted a dominant negative effect on wild-type cells, indicating that they were actively interfering with function. Two truncated versions of FliJ, representing its N- and C-terminal halves, failed to complement and were not dominant. We tested for FliJ self-association by several techniques. Size-exclusion chromatography (Superdex 200) indicated an apparent molecular mass of around 50 kDa, which could reflect either multimerization or an elongated shape or both. Multiangle light scattering gave a peak value of 20 kDa, close to the molecular mass of the monomer. Analytical ultracentrifugation gave evidence for weak self-association as a trimer or tetramer. It was known from previous studies that FliJ interacts with the N-terminal region of FliH, a negative regulator of the ATPase FliI. Using both truncation and deletion versions of FliJ, we now show that it is its C-terminal region that is responsible for this interaction. We also show that FliJ interacts with the soluble cytoplasmic domain of the largest membrane component of the export apparatus, FlhA; although small deletions in FliJ did not interfere with the association, both truncated versions failed to associate, indicating that a substantial amount of the central region of the FliJ sequence participates in the association. We present a model summarizing these multiple interactions.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, USA.
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Fraser
authors.forename: Bertha
authors.initials: B
authors.lastname: González-Pedrajo
authors.forename: Jeremy R H
authors.initials: JR
authors.lastname: Tame
authors.forename: Robert M
authors.initials: RM
authors.lastname: Macnab
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D005407:Flagella / Q000378:metabolism*; D005816:Genetic Complementation Test; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008970:Molecular Weight; D009154:Mutation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012475:Salmonella / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C080688:FlhA protein, Bacteria; D008565:Membrane Proteins; D011994:Recombinant Proteins; C069250:fliH protein, Bacteria; C069253:fliJ protein, Bacteria