Timed light signals provide an external way to test whether an engineered protein switches on and off appropriately. In the optovolution yeast strains, variants that remain in the wrong state can prevent continued growth or cause cell death. Repeated light-driven selection therefore rewards both useful activity and the ability to stop that activity when conditions change.
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22:27evolution is that we were only getting proteins that were on all the time. >> Now, that's going to cause cell death. >> That is no longer the fittest, >> right? M >> in the evolutionary perspective if this protein is on all the time, >> right? >> The cell's going to die. >> We we've basically created it's it's it's it's like in the movies where there's a scene, we've put a a a collar around the protein. Yeah. >> And if it continues doing the thing we don't want it to do, the collar self-implodes. Yeah. Um, but we basically now have a a means by which to prevent a type of protein we don't want to persist. Yes. From persisting. >> Exactly. Isn't that I mean it's such a
23:09such a neat >> thingy thing >> and it's inserting itself because there's a natural process that's already happening. Yeah. >> And we're basically trying to make a portion of the candidate proteins in the entire population not procreate. >> Yeah. Anytime there's a mutation >> Yes. where this thing turns on and stays on, the cell's going to die. Anytime there's a mutation and this thing turns off and stays off, it's going to die. The only way the cell is going to survive is if my protein of interest, which is the thing that I'm trying to evolve, turns on, creates the cycl, and then turns off to stop creating the cycling. Right? And >> now this is the magic of the light.
23:51>> Okay? >> The survival condition is the following. That protein of interest is has a little chromophore. So, it's sensitive to light. >> Okay. >> I'm going to turn it on with light. It's going to turn on. And then when I turn off the light, it's going to turn off. >> Okay. And if it ever goes against that signal that I'm giving, it's it's done. >> It's done. So, so we have this external we're basically trying to uh have the ability to say to say to control the state >> through the light as an external source of of of influence. >> Yes. >> The the internals are such that we've
24:34constructed it that it will always it should when it responds to our light to our external perturbment it will survive. Yeah. If >> if it remains on when we've turned it off, >> then it'll die. And so so now we've basically created a mechanism by which we externally can control the state of the protein >> via light as the mechanism to do so. Because if it no longer responds to our external probing, >> uh it will no longer survive. Yeah. Meaning through the natural evolutionary process, we will kill off the ones that are not what we want to be there. >> Exactly. Yeah. So now we're only keeping
25:16proteins that are toggling on and off. >> On and off >> and and as long as the light is in sync with the cell cycle, which means, you know, it's like over like so it's going to be like on for an hour, then off for an hour, on for an hour, then off for an hour because that's about it's about takes like two hours for yeast to go through the cell cycle and reproduce. And so that's what we're doing. We can drive this oscillator now >> with light. >> It's like you're, you know, pushing on a swing >> and as long as the swing keeps going, you're good. But if the swing stays up, >> that yeast cell is going to die. >> Can I ask a quick clarifying question?
Molecular BiologyProtein EngineeringSynthetic BiologyBioengineering