title: The hydrophobic core of FliG domain II is the stabilizer in the Salmonella flagellar motor.
abstract: The flagellar protein FliG is the major component of the flagellar torque generator, and consists of two separate domains, I and II. Domain I is essential for flagellar assembly, while domain II in the C-terminal region is not essential for flagellar assembly but is dedicated to torque generation. Previously, we found that some fliG mutants were temperature-hypersensitive (hyper-TS) and identified three residues (F236V, D244Y and K273E) on domain II responsible for the temperature-sensitive (TS) phenotype. In this study, we substituted the three residues with all 20 amino acids (X) and analysed the behaviour of the variants at various temperatures. Each group of F236X, D244X and K273X variants gave rise to several hyper-TS mutants. In F236X, only substitution with F and W gave rise to wild-type, while other hydrophobic residues resulted in hyper-TS mutants and hydrophilic residues resulted in non-motile variants. The atomic arrangement around the F236 residue indicated that F236 together with neighbouring residues forms a hydrophobic core in the centre of domain II, which is well conserved among many species. These data suggest that the hydrophobic core may play an essential role in stabilizing the whole structure of domain II, so that changes of physiological conditions in the microenvironment of domain II do not perturb torque generation.
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Manami
authors.initials: M
authors.lastname: Hashimoto
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Momma
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Inaba
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Nakano
authors.affiliation: Department of Life Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan.
authors.forename: Shin-Ichi
authors.initials: SI
authors.lastname: Aizawa
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002942:Circular Dichroism; D005407:Flagella / Q000502:physiology*; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; C075660:Flig protein, Bacteria