Chemicals coded to leave a cell and then come back?

[icakeov]

Is there such a thing of a protein (or some other biochemical) being coded to leave the cell, do something (or not) and then return for another function in the cell? Or in some way go "in and out" throughout its existence?

Or at the least that would "take a leave of absence" and then become active again?

Any thoughts appreciated!

 

[Ygggdrasil]

Sodium and potassium ions in neuronal action potentials come to mind.

 

[icakeov]

Ah of course! Thank you!

 

[BillTre]

Can't think of any proteins that do this off the top of my head.
Certainly ions come and go, but they are not proteins.

A possible protein going out of a cell and returning might be a extracellular protein that stays around the location the cell it can from once it is outside (perhaps an extracellular matrix protein) and is then for some reason degraded as the matrix gets changed. The degraded parts might re-enter the cell and get recycled. Probably not what you were thinking.

Membrane proteins are frequently exposed to the outside of the cell (but still in the cell membrane) and then brought back in by forming vesicles from the surface membrane. These have real functions in and outside of the cell.
However, I would not really consider them outside (as in detached and floating around).

Seems unlikely that any signalling molecule (hormone or transmitter of some kind) would would ever have a reason to con back to the signally source and get inside the cell. However, they could bind to outside receptors to provide feedback on their outside concentrations.

 

[icakeov]

That is super helpful BillTre, thank you!

 

[TeethWhitener]

Neurotransmitters are frequently released from presynaptic neurons, bind to postsynaptic neural receptors to trigger an action potential, and are then released and reabsorbed into the presynaptic neuron. In fact, a large class of antidepressant drugs (selective serotonin reuptake inhibitors, or SSRIs) are designed to regulate this function.

 

[Ygggdrasil]

On the protein side, transferrin could fit the description. Transferrin is an iron-biding protein produced inside of the cell then secreted into the blood, where it helps bind iron ions and regulate iron levels. Transferrin can then bind to the transferrin receptor on cells, which triggers both the receptor and the transferrin to be brought into the cell. The transferrin receptor and other similar receptor proteins could also fit the description because they cycle between the inside of the cell and the outside (though on the outside of the cell, they are still anchored to the plasma membrane, so they don't quite leave the cell).

For a nice diagram of how transferrin & the transferrin receptor are cycled between the inside and outside of the cell to mediate cellular iron uptake, here's a useful figure:

https://file.scirp.org/Html/10-8901284_21593.htm

 

[icakeov]

Transferrin totally hits the mark! Thank you @Ygggdrasil!