Bacterial motors carefully studied; the latest (Introduction)

by David Turell , Saturday, May 27, 2023, 01:55 (337 days ago) @ David Turell

Highly complex methods revealed latest findings:

https://inference-review.com/article/bacterial-swimming

"STUDIES OF THE bacterial flagellar motor were some of the first to take advantage of cryo-EM. David DeRosier and Keiichi Namba used cryo-EM to study the basal body and the flagellar filament, respectively.10 Structural insight into the stator units around the basal body was restricted to negative-stain reconstructions, again with limited resolution.11 Tomography gave additional insight into their organization,12 but the limited resolution of these reconstructions prevented detailed molecular understanding of torque generation.

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"To our great surprise, we found that the stator unit is a complex with a stoichiometry of 5:2 MotA:MotB, and not 4:2 as previously believed.16 This ratio introduces an asymmetry, as 4:2 stoichiometry would most likely have been symmetric. MotA has four helices spanning the inner membrane and a cytoplasmic domain. The part of this domain most distal from the membrane is well conserved and binds the rotor. The five MotA molecules make a nearly symmetric, ringlike structure surrounding the N-terminal helices of two MotB molecules, which contain a universally conserved aspartate residue. Each of the MotB N-terminal helices is followed by a plug helix that lies between two MotA molecules. The two plugs cross over and are thought, based on prior experiments, to block activity of the stator unit. As expected, the channel appears in closed conformation.

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"...result can be explained if it is the rotation of MotA around MotB that drives the rotation of the motor. We proposed that one of the two MotB aspartates—call it MotB1—is protonated and anchored to MotA. This is a high-energy state for MotB1, which would drive MotA rotation were it not for the aspartate of MotB2. This aspartate is both negatively charged and unprotonated: the neutral surface of MotA cannot rotate across it. But when MotB2 accepts a proton from the periplasm, it is neutralized, and rotation of the hydrophobic MotA surface across the neutralized MotB2 aspartate can now occur. After rotation, MotB2 grabs on to MotA in this new position, and MotB1 releases its proton. MotB1 then waits at the cytoplasmic side to pick up a new proton. After these steps, a 36º rotation of the MotA ring around the MotB dimer has occurred. The whole structure is in the same state as before, except that MotB1 and MotB2 have switched roles, so the cycle can begin again.

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"How does this miniature MotAB rotary motor power the rotation of a large flagellum? Upon incorporation in the motor, the C-terminal domains of MotB dimerize and bind to the peptidoglycan layer that forms part of the cell envelope. Peptidoglycan binding is accompanied by the unplugging of the MotAB ion channel, which allows ions to flow from the periplasm to the cytoplasm. Upon ion flow, MotA rotates clockwise around MotB. Given normal swimming conditions, the rotor is engaged at the proximal side of the MotA ring, and the clockwise rotation of MotA rotates the rotor counterclockwise. When all flagella spin counterclockwise, they form a bundle and swim in a straight line.

"Upon chemotactic signaling, a whole signaling cascade takes place and results in the phosphorylation of CheY. Phosphorylated CheY binds to the rotor and switches its conformation. The rotor now interacts with the distal side of the MotA ring. The same clockwise rotation of MotA around MotB induces a clockwise rotation in the motor. One or several flagella change their rotation direction, breaking up the flagellar bundle. The bacterium starts tumbling, until CheY is dephosphorylated and gets released from the rotor and all flagella again spin in the same counterclockwise direction and the bundle reforms.

"Researchers have come a long way since Antonie van Leeuwenhoek observed moving bacteria several centuries ago. They now know bacteria swim using long filaments powered by a bidirectional, rotary proteinaceous motor. They know the molecular makeup of the rotary motor, and that this bidirectional motor is itself driven by unidirectional miniature rotary motors. Yet several unanswered questions still remain. What is the exact energy consumption of the motor—how many ions are used per rotation of MotA around MotB? How can the motor use several stator units? Do they need to act cooperatively, or can single stator units drive rotation even in the presence of other bound but non-active stator units? A combination of single-molecule light microscopy, biophysical experiments, and cryo-electron tomography is likely necessary to answer these questions."

Comment: a microscopic bacterial motor just like the ones we make macroscopically, down to what each molecule does. This is the favorite ID example of what must be designed by a mind. The quality of design is the equal of what we create. If bacteria came first, can you imagine how complex first life was in the very beginning? Remember Archaea came first and they had flagella.