title: Identification of the Key Sequence in the FliK C-Terminal Domain for Substrate Specificity Switching in the Flagellar Protein Secretion.
abstract: The flagellar hook is a short tubular structure located between the external filament and the membrane-bound basal body. The average hook length is 55 nm and is determined by the soluble protein FliK and the integral membrane protein FlhB. Hook elongation is terminated by FliK-mediated cessation of hook protein secretion, followed by the secretion of filamentous proteins. This process is referred to as the substrate specificity switch. Switching of the secretion modes results from a direct interaction between the FliK C-terminal domain (FliKC) and the secretion gate in FlhB. FliKC consists of two α-helices and four β-strands. Loop 2 connects the first two β-sheets and contains a conserved sequence of 9 residues. Genetic and physiological analyses of various fliK partial deletion mutants pointed to loop 2 as essential for induction of a conformational change in the FlhB gate. We constructed single-amino-acid substitutions in the conserved region of loop 2 of FliK and discovered that the loop sequence LRL is essential for the timely switching of secretion modes.
  
  
  OBJECTIVE
  Flagellar protein secretion is controlled by the soluble protein FliK. We discovered that the loop 2 sequence LRL in the FliK C terminus was essential for timely switching of secretion modes. This mechanism is applicable to type three secretions systems that secrete virulence factors in bacterial pathogens.
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Uchida
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Dono
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima, Japan aizawa@pu-hiroshima.ac.jp.
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Aizawa
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005408:Flagellin / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; C099486:FliK protein, Bacteria; D005408:Flagellin