Hypothesis on why ATP synthase changes rotation

[Giulia Barbarito]

Hello,

it is known that ATP synthase changes rotation when if has to create ATP from when it hydrolyzes it. 

My question is: what could be a hypothesis for this mechanism?

My only idea is an hypothesis against it: the bacterial flagellar motor can shift the direction of rotation between forward and reverse without changing the direction of proton movement through the membrane.

I studied the experiments, but i would like to find the first hypotheses that then gave birth to these experiments.

thanks.

[Dagl1]

https://link.springer.com/article/10.1007%2Fs00232-014-9760-y

This is what you are referring too? 

I may be thinking too simply but wouldn't the reason that this happens just be energy-conversation? If rotating sideways in the x direction allows protons to move from a higher (potential?) energy state to a lower one, and that energy is then bound to ATP. Then if you want to do the opposite, the rotation will also be in the y (the other) direction. As now we want to use the energy contained in ATP to produce protons with higher (potential?) energy. 

I think after a brief look that the reason is the difference in structure, bacterial flagellar motors have quite a different structure and contain a specific 'C ring' which acts like a gear (think of setting your car in reverse). Also it is important to note that they only move clockwise for a few rotations and then change back to regular counterclockwise rotation, if I have interpreted this right.

Oh I recommend adding sources to your questions, it makes it easier for people to look stuff up and help you!

https://www.sciencedirect.com/science/article/pii/S2001037019302338#bb0010

(source of the ATP synthase picture: https://www.nature.com/articles/46193)

-Dagl

[Dagl1]

Addition:

and here is another source about it, its quite interesting, thanks for asking!

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4938800/

-Dagl

[BabcockHall]

My working hypothesis is that the flagellar rotor can rotate in either direction because FliG has multiple conformations owing to what might be termed hinges.  I am unaware that ATP synthase has a similar property.

[Dagl1]

Yes that, and I believe I read that the ATP synthase rotor is asymmetric, while I thought the MotA/MotB of the bacterial flagellum was symmetric but now I can't really find any evidence for that (maybe there is, but can't find it easily).

[BabcockHall]

I don't know much about MotA/MotB other than there was a nice genetic suppression study done on the generation of torque some years back.  Can you explain what you mean by symmetric?

[Dagl1]

The subunits that let through protons across membranes. ATP synthase has asymmetric subunits which is one of the reasons that movement 1 way and movement another way facilitates 2 separate processes.

In the case of MotA/MotB, I thought that I once saw a picture that showed the inner channel to be symmetric (so that proton movement could be facilitated in both directions). 

Basically, when ATP synthase turns the other way, by definition we are using energy to move protons towards higher potential energy. But the flagellum just moves the protons from [high] to [low] regardless of the direction the subunits are going and thus always produces energy. Please note that the gearbox idea on its own should suffice and that I cannot find this picture or something like it, so I may have misremembered or the source was not as truthful as I thought it to be.

[Giulia Barbarito]

I've read something about the asymmetry of the a subunit, and how this produces opposites rotations in ATP synthesis and hydrolysis. Honestly, I don't understand how asymmetry can make a difference from symmetry. 

Thank you for your kind help.

 

[BabcockHall]

On 1/25/2020 at 4:07 AM, Dagl1 said:

In the case of MotA/MotB, I thought that I once saw a picture that showed the inner channel to be symmetric (so that proton movement could be facilitated in both directions). 
 

As far as I am aware, protons only flow in one direction, outside to inside.  The key to how the flagellar motor rotates in both directions may lie in the flexibility of FliG.

[Dagl1]

Ye could definitely be the case, I am not very familiar with the details.