Load-sensitive coupling of proton translocation and torque generation in the bacterial flagellar motor

Yong Suk Che, Shuichi Nakamura, Yusuke V. Morimoto, Nobunori Kami-ike, Keiichi Namba, Tohru Minamino

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


The Salmonella 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 Asp33 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(D33E) mutation dramatically alters motor performance in response to changes in external load. Rotation speeds of the MotA/B(D33E) and MotA(V35F)/B(D33E) 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 D33E 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 Asp33 of MotB is critical for this co-ordinated proton translocation.

Original languageEnglish
Pages (from-to)175-184
Number of pages10
JournalMolecular Microbiology
Issue number1
Publication statusPublished - 2014 Jan

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


Dive into the research topics of 'Load-sensitive coupling of proton translocation and torque generation in the bacterial flagellar motor'. Together they form a unique fingerprint.

Cite this