title: Two-ball structure of the flagellar hook-length control protein FliK as revealed by high-speed atomic force microscopy.
abstract: The bacterial flagellar hook is a short and uniquely curved tube that connects the basal body to the filament. Hook length is controlled at 55 nm on average by a soluble protein FliK in Salmonella enterica serovar Typhimurium. The N-terminal segment of FliK responsible for measuring the hook length is considered to be intrinsically disordered. Here, we show by high-speed atomic force microscopy that a FliK molecule in solution takes on a shape of two balls linked by a flexible string; the larger ball corresponds to the N-terminal region and the smaller one corresponds to the C-terminal region. The N-terminal domain is stable but the C-terminal domain fluctuates in shape. Based on these and other features of FliK, we propose that the folding of the N-terminal segment at the tip of the growing hook plays a major role in determining the minimal length of the hook.
authors.affiliation: Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa 920-1192, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kodera
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Uchida
authors.affiliation: Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa 920-1192, Japan; Department of Physics, Kanazawa University, Kanazawa 920-1192, Japan. Electronic address: tando@staff.kanazawa-u.ac.jp.
authors.forename: Toshio
authors.initials: T
authors.lastname: Ando
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan. Electronic address: aizawa@pu-hiroshima.ac.jp.
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Aizawa
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D005407:Flagella / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force / Q000379:methods*; D015394:Molecular Structure; D017510:Protein Folding; D055550:Protein Stability; D012486:Salmonella typhimurium / Q000737:chemistry / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; C099486:FliK protein, Bacteria
keywords: AFM; FliK; Salmonella enterica serovar Typhimurium; intrinsically disordered structure; secretion substrate specificity