Mirror life and backward biology

We now know what chirality is - but what about mirror life itself? Jonathan Jarry - a science communicator with McGill University's Office for Science and Society - has just written an excellent piece on exactly that, and I've been speaking with him…

Jonathan - When we talk about life as we know it, which includes bacteria, plant life, animals, us, it can be boiled down to DNA molecules, can be transcribed into RNA, and that RNA is translated into proteins and proteins are the effectors of the cell. They play all sorts of roles. But when we zoom in on the building blocks that make up these molecules, we realise that some of them have a handedness.

For example, DNA has a sugar backbone and that sugar molecule, if you manage to put it in front of a mirror, would have a mirror image, just like your left-hand is a mirror image of your right-hand. And when we look at what proteins are made of, which are amino acids, almost all of them are left-handed. And what's really interesting is that we don't see their mirror images in nature.

We don't see the left-handed version of this particular sugar, nor do we see the right-handed version of these amino acids, but we can create them in the lab.

Chris - So it's fair to say these molecules, the right-handed, left-handed forms, they exist chemically, they can exist, they do exist, but life doesn't use them. It has settled on a handedness, which presumably, given that it's in all the different realms of life on Earth, was a decision, in inverted commas, that life made very early on during evolution. And it's sort of fixed, that we've centred on using left-handed proteins, right-handed genetic molecules.

Jonathan - Essentially, yes, as far as we know, we have not seen the reverse of the mirror image of that in the world around us.

Chris - And do we see any examples of where this handedness of molecules is at play in biology, apart from the fact that life depends on building things with it that way? But do we actually see any other tangible examples of this at play, where it really matters whether you've got right-handed or left-handed molecules?

Jonathan - Well, basically, if we think of our immune system, for instance, a lot of the functions that it serves, defending us against these microorganisms that can cause disease, a lot of these functions are based around chirality, around handedness, which is that something in your immune system needs to bind something of this microorganism. There needs to be some kind of a handshake. And it works because these microorganisms, the kinds of molecules that we're used to, they're also made of. But if they weren't, that handshake might not be able to happen.

Chris - So, in the same way that Phillip shook my hand outside the Eagle Pub, and his right hand met my right hand, if I got infected with one of these bacteria, that was a mirror image bacterium, then it would be using the wrong handedness and it'd be like me trying to shake a right-hand with a left-hand.

Jonathan - Exactly. And so in theory, this would make this mirror bacterium invisible to you. And so there's an argument to be made that if it were to produce a toxin, for instance, that that toxin wouldn't be able to harm you, because it wouldn't be recognised by your body.

However, there was also this idea that this mirror bacterium, if it were to be growing inside of you, could be growing a bit like a cancer. And it might create a mass that might sort of push against some of your organs and lead to disease.

Chris - Is there a real possibility then that they would just exist alongside nature as we know it, and we would not be able to effectively see them, and we wouldn't be able to deal with them?

Jonathan - That's the thing. We don't really know what would happen because, in a way, the fact that their handedness is the opposite of what we're used to, it would create a bit of an invisibility field around them. They wouldn't be able to interact much with the world as we know it. They would be able to feed because there are nutrients that are what we call achiral. They don't have mirror images, or their mirror image is exactly the same as what they are, things like glycerol and butyric acid. Beyond that, what would happen to the environment? I mean, there is again, the potential that these mirror bacteria could invade the environment and without having any natural predator, sort of take over entire ecosystems and disrupt animal and plant life in certain ways. Those are things that scientists who are working in this field are getting increasingly concerned with.

Chris - How hard would it be though to do that? I don't mean as in for the organism to take over, I mean, for a scientist working in a lab to produce an entirely synthetic organism that is the mirror image, chemically speaking, of an equivalent that we already have?

Jonathan - There are two main ways of creating a bacterium like this, because some of these big molecules have been created, the mirror images of certain proteins have been created. And if you make enough of them, you can imagine at some point you could create a mirror microorganism like a mirror bacterium. And again, there are two ways of going about this. You could create all of these molecules in the lab, put them inside of a membrane, and hope that - like with Frankenstein's creature - it sort of comes alive. Or you could take a regular bacterium and reprogramme its DNA so that it would start making mirror molecules. So that eventually, like the Ship of Theseus, all of its parts end up being replaced by mirror molecules, and now it has become a mirror bacterium. And there was a report that was released recently by scientists who are concerned about the possibility of this. And their best guess is that, within 20 years, this could be possible.

Chris - If you could make a protein that had some amino acids that twisted the wrong way, so they were invisible or couldn't be broken down by normal digestive processes in the body, could you not make much better, more potent drugs? Because those proteins could do things, but they would be immune to the body's normal mechanisms of elimination.

Jonathan - Precisely. So, many of the older drugs that we have, they are not proteins, but many modern medications are these long chains of amino acids. We can think of Ozempic / Wegovy - that's a chain of amino acids. Many targeted cancer drugs are also chains of amino acids. There's a whole slew of biologics that help with autoimmune diseases like rheumatoid arthritis, psoriasis. These are also chains of amino acids. And as you pointed out, scientists are now retooling proteins and some of these drugs to replace a left-handed amino acid with a right-handed one, because when you do that, the enzymes in your body can't recognise the molecule quite as well. And so the idea would be that you would need a lower dose and fewer injections because that drug would stay in your body for a longer period of time before being degraded. And you could thus benefit from it for a longer time in between doses.

Chris - Where does this leave us then, Jonathan? Because on the one hand, you can see that this sounds like it could get dodgy and dicey quite quickly and there could be an unmitigated disaster awaiting mankind if we do it. On the other hand, as you've just said, there could be some enormous potential benefits. So is there a middle ground or is it just too dangerous and we don't play in this space?

Jonathan - Well, there's a difference between creating mirror molecules and creating a full-on mirror microorganism. It's my interpretation that that is where the line was drawn by the authors of that article that was penned last Christmas called “Confronting Risks of Mirror Life.” What I really hope happens following the publication of this piece is that there is even more discussion happening within these fields of study to decide what are the dangers, what do we know and where should we draw that line?