Papers - NISHIKINO Tatsuro
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The role of conserved charged residues in the bidirectional rotation of the bacterial flagellar motor. Reviewed International journal
Yasuhiro Onoue, Norihiro Takekawa, Tatsuro Nishikino, Seiji Kojima, Michio Homma
MicrobiologyOpen 7 ( 4 ) e00587 2018.08
Language：English
Many bacteria rotate their flagella both counterclockwise (CCW) and clockwise (CW) to achieve swimming toward attractants or away from repellents. Highly conserved charged residues are important for that motility, which suggests that electrostatic interactions are crucial for the rotor-stator function. It remains unclear if those residues contribute equally to rotation in the CCW and CW directions. To address this uncertainty, in this study, we expressed chimeric rotors and stators from Vibrio alginolyticus and Escherichia coli in E. coli, and measured the rotational speed of each motor in both directions using a tethered-cell assay. In wild-type cells, the rotational speeds in both directions were equal, as demonstrated previously. Some charge-neutralizing residue replacements in the stator decreased the rotational speed in both directions to the same extent. However, mutations in two charged residues in the rotor decreased the rotational speed only in the CCW direction. Subsequent analysis and previous results suggest that these amino acid residues are involved in supporting the conformation of the rotor, which is important for proper torque generation in the CCW direction.
DOI： 10.1002/mbo3.587
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Serine suppresses the motor function of a periplasmic PomB mutation in the Vibrio flagella stator. Reviewed International journal
Tatsuro Nishikino, Shiwei Zhu, Norihiro Takekawa, Seiji Kojima, Yasuhiro Onoue, Michio Homma
Genes to cells : devoted to molecular & cellular mechanisms 21 ( 5 ) 505 - 16 2016.05
Language：English
The flagellar motor of Vibrio alginolyticus is made of two parts: a stator consisting of proteins PomA and PomB, and a rotor whose main component is FliG. The interaction between FliG and PomA generates torque for flagellar rotation. Based on cross-linking experiments of double-Cys mutants of PomB, we previously proposed that a conformational change in the periplasmic region of PomB caused stator activation. Double-Cys mutants lost their motility due to an intramolecular disulfide bridge. In this study, we found that the addition of serine, a chemotactic attractant, to a PomB(L160C/I186C) mutant restored motility without cleaving the disulfide bridge. We speculate that serine changed the rotor (FliG) conformation, affecting rotational direction. Combined with the counterclockwise (CCW)-biased mutation FliG(G214S), motility of PomB(L160C/I186C) was restored without the addition of serine. Likewise, motility was restored without serine in Che(-) mutants, in either a CCW-locked or clockwise (CW)-locked strain. In contrast, in a ΔcheY (CCW-locked) strain, Vibrio (L160C/I186C) required serine to be rescued. We speculate that CheY affects stator conformation and motility restoration by serine is independent on the chemotaxis signaling pathway.
DOI： 10.1111/gtc.12357
