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Load‐sensitive coupling of proton translocation and torque generation in the bacterial flagellar motor
Author(s) -
Che YongSuk,
Nakamura Shuichi,
Morimoto Yusuke V.,
Kamiike Nobunori,
Namba Keiichi,
Minamino Tohru
Publication year - 2014
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.12453
Subject(s) - stator , proton , mutant , biophysics , biology , rotor (electric) , coupling (piping) , proton transport , control theory (sociology) , physics , materials science , genetics , computer science , gene , control (management) , quantum mechanics , artificial intelligence , metallurgy
Summary The S almonella flagellar motor consists of a rotor and about a dozen stator elements. Each stator element, consisting of MotA and MotB , acts as a proton channel to couple proton flow with torque generation. A highly conserved Asp 33 residue of MotB is directly involved in the energy coupling mechanism, but it remains unknown how it carries out this function. Here, we show that the MotB ( D 33 E ) mutation dramatically alters motor performance in response to changes in external load. Rotation speeds of the MotA / B ( D 33 E ) and MotA ( V 35 F )/ B ( D 33 E ) motors were markedly slower than the wild‐type motor and fluctuated considerably at low load but not at high load, whereas the rotation rate of the wild‐type motor was stable at any load. At low load, pausing events were frequently observed in both mutant motors. The proton conductivities of these mutant stator channels in their ‘unplugged’ forms were only half of the conductivity of the wild‐type channel. These results suggest that the D 33 E mutation induces a load‐dependent inactivation of the MotA / B complex. We propose that the stator element is a load‐sensitive proton channel that efficiently couples proton translocation with torque generation and that Asp 33 of MotB is critical for this co‐ordinated proton translocation.