PT - JOURNAL ARTICLE AU - Terahara, Naoya AU - Kodera, Noriyuki AU - Uchihashi, Takayuki AU - Ando, Toshio AU - Namba, Keiichi AU - Minamino, Tohru TI - Na<sup>+</sup>-induced structural transition of MotPS for stator assembly of the <em>Bacillus</em> flagellar motor AID - 10.1126/sciadv.aao4119 DP - 2017 Nov 01 TA - Science Advances PG - eaao4119 VI - 3 IP - 11 4099 - http://advances.sciencemag.org/content/3/11/eaao4119.short 4100 - http://advances.sciencemag.org/content/3/11/eaao4119.full SO - Sci Adv2017 Nov 01; 3 AB - The bacterial flagellar motor consists of a rotor and a dozen stator units and regulates the number of active stator units around the rotor in response to changes in the environment. The MotPS complex is a Na+-type stator unit in the Bacillus subtilis flagellar motor and binds to the peptidoglycan layer through the peptidoglycan-binding (PGB) domain of MotS to act as the stator. The MotPS complex is activated in response to an increase in the Na+ concentration in the environment, but the mechanism of this activation has remained unknown. We report that activation occurs by a Na+-induced folding and dimer formation of the PGB domain of MotS, as revealed in real-time imaging by high-speed atomic force microscopy. The MotPS complex showed two distinct ellipsoid domains connected by a flexible linker. A smaller domain, corresponding to the PGB domain, became structured and unstructured in the presence and absence of 150 mM NaCl, respectively. When the amino-terminal portion of the PGB domain adopted a partially stretched conformation in the presence of NaCl, the center-to-center distance between these two domains increased by up to 5 nm, allowing the PGB domain to reach and bind to the peptidoglycan layer. We propose that assembly of the MotPS complex into a motor proceeds by means of Na+-induced structural transitions of its PGB domain.