Mirror mirror biology

Scientists have engineered a "mirror" DNA polymerase

I love labs that work on esoteric corners of science. Understudied niches with few immediate application are where the most interesting science happens. Perhaps unfairly, I categorize the Zhu lab as one of these niche labs. Their topic of interest is mirror-image biology.

Their studies and experiments are best explained by analogy: When you look into a mirror, you see a familiar yet different version of yourself. Your mirror image looks like a fully functioning human being, capable of doing all the things that you are capable of, however it’s not quite you. There are two versions of you, the real you and the mirror version of you.

This curiosity carries down to the molecular level. When it comes to fundamental biological processes, such as DNA replication and transcription (the process of going from DNA to RNA), there are two possible forms that these molecules can exist in. You can think of these two possibilities as either mirror images or left-handed and right-handed molecules. Molecular biologists and chemists call this chirality.

For an unknown reason, in all discovered organisms we only observe one of these two molecular possibilities. The Zhu lab has tasked themselves with asking the question: is a mirror universe where biological processes are based on the opposite chirality possible? and can we build it?

Well, the answer is probably yes. In their latest paper, the team engineered a mirror-image DNA polymerase (the molecule responsible for replicating DNA) and showed that it works efficiently.

In one experiment, the team stored a mirror-DNA barcode in water from a local pond. That is, they encoded some known sequence in DNA molecules that are the mirror image of our “normal” DNA. The intention of using pond-water is to show that mirror-DNA can co-exist with existing biology but remain unprocessed, is not degraded and is biologically inert.

Sure enough, after 1 year of storage, the mirror-DNA could still be detected in the pond water sample. They compared this to a pond water sample containing regular DNA. After just 1 day of storage, the regular DNA could no longer be detected. This can be explained by the regular DNA being degraded and processed by the various proteins and enzymes in the pond water. These same proteins are unable to process the mirror-DNA, making it a very stable molecule.

I’m almost reluctant to discuss the potential applications for mirror-DNA. Not because it’s dangerous (it’s probably not), but because I think discussing applications takes away from the beauty of this lab’s work. History is filled with discoveries that had seemingly few applications, later leading to huge breakthroughs and advances. Here, the Zhu lab set out to answer a very fundamental question about biology as we know it. The beauty of their work is that they answered it by building. Answering such a fundamental question should be enough, with or without immediate applications.

Having said that, one immediate application of mirror-DNA is for long term storage. Other labs have shown that DNA can be used to efficiently encode data, but degradation of the DNA in long term storage is a problem. Traditional digital storage methods also suffer from degradation problems when the timescale for storage is in the tens or hundreds of years. If mirror-DNA is relatively inert, it could be used to store data alongside other organisms at room temperature with minimal data loss.

At the very least, demonstrating that an efficient mirror DNA polymerase is possible opens up the entire mirror biology field for further exploration. Now that a proof of concept has been built, other labs will want to confirm the results and then take this further by building their own mirror-molecules. One day in the future we could possess mirror versions of all the molecules necessary for life, enabling us to build mirror organisms.

A link to the study.