Determination of Local pH Differences within Living Cells by High-resolution pH Imaging Based on pH-sensitive GFP Derivative, pHluorin(M153R).

The bacterial flagellar type III protein export apparatus is composed of a transmembrane export gate complex and a cytoplasmic ATPase complex. The export apparatus requires ATP hydrolysis and the proton motive force across the cytoplasmic membrane to unfold and transport flagellar component proteins for the construction of the bacterial flagellum (Minamino, 2014). The export apparatus is a proton/protein antiporter that couples the proton flow with protein transport through the gate complex ( Minamino , 2011 ).

Load- and polysaccharide-dependent activation of the Na-type MotPS stator in the Bacillus subtilis flagellar motor.

The flagellar motor of Bacillus subtilis possesses two distinct H-type MotAB and Na-type MotPS stators. In contrast to the MotAB motor, the MotPS motor functions efficiently at elevated viscosity in the presence of 200 mM NaCl. Here, we analyzed the torque-speed relationship of the Bacillus MotAB and MotPS motors over a wide range of external loads.

High-Resolution pH Imaging of Living Bacterial Cells To Detect Local pH Differences.

Unlabelled: Protons are utilized for various biological activities such as energy transduction and cell signaling. For construction of the bacterial flagellum, a type III export apparatus utilizes ATP and proton motive force to drive flagellar protein export, but the energy transduction mechanism remains unclear. Here, we have developed a high-resolution pH imaging system to measure local pH differences within living Salmonella enterica cells, especially in close proximity to the cytoplasmic membrane and the export apparatus.

Assembly dynamics and the roles of FliI ATPase of the bacterial flagellar export apparatus.

For construction of the bacterial flagellum, FliI ATPase forms the FliH2-FliI complex in the cytoplasm and localizes to the flagellar basal body (FBB) through the interaction of FliH with a C ring protein, FliN. FliI also assembles into a homo-hexamer to promote initial entry of export substrates into the export gate. The interaction of FliH with an export gate protein, FlhA, is required for stable anchoring of the FliI6 ring to the gate.

Assembly and stoichiometry of FliF and FlhA in Salmonella flagellar basal body.

The bacterial flagellar export apparatus is required for the construction of the bacterial flagella beyond the cytoplasmic membrane. The membrane-embedded part of the export apparatus, which consists of FlhA, FlhB, FliO, FliP, FliQ and FliR, is located in the central pore of the MS ring formed by 26 copies of FliF. The C-terminal cytoplasmic domain of FlhA is located in the centre of the cavity within the C ring made of FliG, FliM and FliN.

Effect of the MotB(D33N) mutation on stator assembly and rotation of the proton-driven bacterial flagellar motor.

The bacterial flagellar motor generates torque by converting the energy of proton translocation through the transmembrane proton channel of the stator complex formed by MotA and MotB. The MotA/B complex is thought to be anchored to the peptidoglycan (PG) layer through the PG-binding domain of MotB to act as the stator. The stator units dynamically associate with and dissociate from the motor during flagellar motor rotation, and an electrostatic interaction between MotA and a rotor protein FliG is required for efficient stator assembly.

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

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.

Populational heterogeneity vs. temporal fluctuation in Escherichia coli flagellar motor switching.

The dynamic switching of the bacterial flagellar motor regulates cell motility in bacterial chemotaxis. It has been reported under physiological conditions that the switching bias of the flagellar motor undergoes large temporal fluctuations, which reflects noise propagating in the chemotactic signaling network. On the other hand, nongenetic heterogeneity is also observed in flagellar motor switching, as a large group of switching motors show different switching bias and frequency under the same physiological condition.

The C-terminal periplasmic domain of MotB is responsible for load-dependent control of the number of stators of the bacterial flagellar motor.

The bacterial flagellar motor is made of a rotor and stators. In Salmonella it is thought that about a dozen MotA/B complexes are anchored to the peptidoglycan layer around the motor through the C-terminal peptidoglycan-binding domain of MotB to become active stators as well as proton channels. MotB consists of 309 residues, forming a single transmembrane helix (30-50), a stalk (51-100) and a C-terminal peptidoglycan-binding domain (101-309).

Charged residues in the cytoplasmic loop of MotA are required for stator assembly into the bacterial flagellar motor.

MotA and MotB form a transmembrane proton channel that acts as the stator of the bacterial flagellar motor to couple proton flow with torque generation. The C-terminal periplasmic domain of MotB plays a role in anchoring the stators to the motor. However, it remains unclear where their initial binding sites are.

Evidence for symmetry in the elementary process of bidirectional torque generation by the bacterial flagellar motor.

The bacterial flagellar motor can rotate in both counterclockwise (CCW) and clockwise (CW) directions. It has been shown that the sodium ion-driven chimeric flagellar motor rotates with 26 steps per revolution, which corresponds to the number of FliG subunits that form part of the rotor ring, but the size of the backward step is smaller than the forward one. Here we report that the proton-driven flagellar motor of Salmonella also rotates with 26 steps per revolution but symmetrical in both CCW and CW directions with occasional smaller backward steps in both directions.

Roles of the extreme N-terminal region of FliH for efficient localization of the FliH-FliI complex to the bacterial flagellar type III export apparatus.

Most bacterial flagellar proteins are exported by the flagellar type III protein export apparatus for their self-assembly. FliI ATPase forms a complex with its regulator FliH and facilitates initial entry of export substrates to the export gate composed of six integral membrane proteins. The FliH-FliI complex also binds to the C ring of the basal body through a FliH-FliN interaction for efficient export.

Role of a conserved prolyl residue (Pro173) of MotA in the mechanochemical reaction cycle of the proton-driven flagellar motor of Salmonella.

The MotA/B complex acts as the stator of the proton-driven bacterial flagellar motor. Proton translocation through the stator complex is efficiently coupled with torque generation by the stator-rotor interactions. In Salmonella enterica serovar Typhimurium, the highly conserved Pro173 residue of MotA is close to the absolutely conserved Asp33 residue of MotB, which is believed to be a proton-binding site.

Effect of intracellular pH on the torque-speed relationship of bacterial proton-driven flagellar motor.

Bacterial flagella responsible for motility are driven by rotary motors powered by the electrochemical potential difference of specific ions across the cytoplasmic membrane. The stator of proton-driven flagellar motor converts proton influx into mechanical work. However, the energy conversion mechanism remains unclear.

Suppressor analysis of the MotB(D33E) mutation to probe bacterial flagellar motor dynamics coupled with proton translocation.

MotA and MotB form the stator of the proton-driven bacterial flagellar motor, which conducts protons and couples proton flow with motor rotation. Asp-33 of Salmonella enterica serovar Typhimurium MotB, which is a putative proton-binding site, is critical for torque generation. However, the mechanism of energy coupling remains unknown.

Large-scale screening of Arabidopsis circadian clock mutants by a high-throughput real-time bioluminescence monitoring system.

Using a high-throughput real-time bioluminescence monitoring system, we screened large numbers of Arabidopsis thaliana mutants for extensively altered circadian rhythms. We constructed reporter genes by fusing a promoter of an Arabidopsis flowering-time gene - either GIGANTEA (GI) or FLOWERING LOCUS T (FT) - to a modified firefly luciferase gene (LUC(+)), and we transferred the fusion gene (P(GI)::LUC(+) or P(FT)::LUC(+)) into the Arabidopsis genome. After mutagenesis with ethyl methanesulfonate, 50 000 M(2) seedlings carrying the P(GI)::LUC(+) and 50 000 carrying P(FT)::LUC(+) were screened their bioluminescence rhythms.