Abstract
The bacterial flagellar motor is a sophisticated nanomachine embedded in the cell envelope. The flagellar motor is driven by an electrochemical gradient of cations such as H+, Na+, and K+ through ion channels in stator complexes embedded in the cell membrane. The flagellum is believed to rotate as a result of electrostatic interaction forces between the stator and the rotor. In bacteria of the genus Bacillus and related species, the single transmembrane segment of MotB-type subunit protein (MotB and MotS) is critical for the selection of the H+ and Na+ coupling ions. Here, we constructed and characterized several hybrid stators combined with single Na+-coupled and dual Na+- and K+-coupled stator subunits, and we report that the MotP subunit is critical for the selection of K+. This result suggested that the K+ selectivity of the MotP/MotS complexes evolved from the single Na+-coupled stator MotP/MotS complexes. This finding will promote the understanding of the evolution of flagellar motors and the molecular mechanisms of coupling ion selectivity.
Highlights
Many motile bacteria have a spiral flagellum as a locomotor and move in the environment by rotating one or more flagellar bundles
B. alcalophilus and B.Tprsiesudmoefidrmiuums sahtowpHed9N.0a+[-22a,n4d0]K. +B-.dterpyepnoxdyelnictoalandshoonwlyedNao+n-ldyepKe+n-ddeepnetngdreonwt thgrroewspthec. tTivheilsy result in Trisinmdeicdaituemd tahtapt HB. t9r.y0p[o2x2y,l4i0co].laBp.rterfyeprsoxtyoliucsoelaKs+hroawtheedr tohnalny NKa++-dfoerpgernodwentht ignroawlktahli.nTe heinsvrierosunlmt ents. indicated that B. trypoxylicola prefers to use K+ rather than Na+ for growth in alkaline environments
To K+ andsuNmam+.arize these results, it was suggested that B. trypoxylicola has a flagellar motor coupled to both
Summary
Many motile bacteria have a spiral flagellum as a locomotor and move in the environment by rotating one or more flagellar bundles. The basal body of the flagellar motor consists of a rotor and a stator. The stator complex is composed of two subunits (MotA-type and MotB-type) formed at a ratio of 4:2, functions as an ion channel and anchors to the cell wall through a putative peptidoglycan-binding (PGB) motif in the periplasmic domain of a MotB-type protein. Marine Vibrio species PomA/PomB complex and alkaliphilic Bacillus MotP/MotS complex are Na+ driven flagellar motors, respectively [12,13,14,15]. E. coli and alkaliphilic Bacillus pseudofirmus have only one type of Mot complex in the motor [16,17,18]. In 2008, the alkaliphilic Bacillus clausii KSM-K16 was identified as the first bacterium to have a single stator rotor that uses both H+ and Na+ for ion coupling depending on the Ph [21]. TCA20 uses Ca2+ and Mg2+ as coupling ions for flagellar rotation [3,23]
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