"As imaging improves, so does knowledge of the workings of the bacterial flagellum. Two new papers point out new findings about these outboard motors that contribute to the argument that they are irreducibly complex and intelligently designed.
One paper in PNAS by German scientists explores the advantage of having two flagella, one at the rear and another one or two on the sides. If you were a blind bacterium trying to find your way up a gradient, you would only have one trick in your steering kit: the "run-reverse-flick" move. Trouble is, when you operate that move, it often turns you 90 degrees. That's not helpful when you want to make progress up the gradient. The scientists found that having a secondary flagellum reduces that angle, even when it doesn't not provide extra power.
During assembly of a flagellum, the bacterium must avoid starting the engines before they are anchored in place. This is similar to fastening an outboard motor to a boat: turning the motor on could be dangerous. Another paper in PNAS describes how a particular protein in the stator plugs its ion channel until the stator is properly positioned in the membrane. In essence, it waits for a signal that assembly is complete, then undergoes a conformational change that allows the ions that drive the motor to flow.
In this excerpt from their final discussion, notice how they describe the stepwise, coordinated assembly of parts before the ion-drive motor goes into action:
My frame was not hidden from You,
When I was made in secret,
Psalm 139:15 NKJV
One paper in PNAS by German scientists explores the advantage of having two flagella, one at the rear and another one or two on the sides. If you were a blind bacterium trying to find your way up a gradient, you would only have one trick in your steering kit: the "run-reverse-flick" move. Trouble is, when you operate that move, it often turns you 90 degrees. That's not helpful when you want to make progress up the gradient. The scientists found that having a secondary flagellum reduces that angle, even when it doesn't not provide extra power.
Stator is the energy-converting membrane protein complex in the flagellar motor. Its ion-conducting activity is only activated when incorporated into the motor, but the mechanism for assembly-coupled activation remains a mystery. In this study, we solved the structure of a C-terminal fragment of the sodium-driven stator protein PomB (PomBC), the region responsible for anchoring the stator unit, at 2.0-Å resolution. In vivo disulfide cross-linking studies of PomB double-Cys mutants and their motility assay suggested that the N-terminal region of PomBC changes its conformation, which is expected for MotB, the counterpart of PomB in the proton-driven Salmonella motor, in the final step of the stator assembly around the rotor.
It's remarkable that scientists can now look at parts of machines at two angstrom resolution -- two 10 billionths of a meter!
On the basis of this study and together with our previous results, we propose a model for activation mechanism of the Vibrio sodium-driven motor (Fig. S6).
The stator diffusing in the cell membrane is in an inactive state.
When the stator reaches around the rotor, PomA interacts with FliG.
This interaction triggers opening of a"plug," allowing sodium ion to translocate into the channel of the stator. The sodium flow may induce the binding of PomB to the T-ring.
This step probably includes a conformational change of the disordered N-terminal region of the PEM.
After that, the N-terminal two-thirds of α1 changes its conformation to an extended form to anchor to the PG layer [peptidoglycan layer, part of the external membrane]." ENV
My frame was not hidden from You,
When I was made in secret,
Psalm 139:15 NKJV
