Xenobiology: Life doesn’t Need DNA or RNA

Our assumptions about what is required for biological processes – the ‘secret of life’ – may need some further revision“ Dr Alex Taylor, University of Cambridge

Among other things, Rosetta’s and Philae’s mission of boarding the comet 67P/C-G was to find traces of organic molecules and water, which could confirm the theory that water and life on Earth originated on these comet and asteroid-like celestial bodies. Although the mission itself was successful, and praised around the world as one of the greatest achievements of the humanity in space explorations, none of the aforementioned goals were achieved. The spacecrafts were conveniently named after famous objects used to decipher Egyptian hieroglyphs, Rosetta Stone and Philae obelisk. But, it appears that decoding origins of life on Earth doesn’t take traveling into deep space.

Dr Philipp Holliger, a researcher at the Laboratory of Molecular Biology, Cambridge, and his colleagues were able to produce enzymes, vital catalysts of life as we know it, from genetic material created in the lab. These synthetic enzymes do not contain DNA or RNA, but a nucleic acid that cannot be found in nature, a synthetic alternative called XNA (Xeno Nucleic Acid). Until recently, DNA and RNA were the only known molecules able to store genetic information, and, along with proteins, the only biomolecules capable of forming enzymes. It is thought that life on Earth was set in motion once the segment of RNA was able to successfully copy itself. Xenobiology has set itself the task to investigate if life on our planet only ‘accidentally’ evolved on DNA-RNA-protein bases, or there could be other ways in which life could appear.
Previously, Dr Holliger’s team was the first one to successfully synthesize XNA (Xeno Nucleic Acid) in the laboratory, using the same constructs (nucleotides) as those present in DNA and RNA: adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U). Researchers replaced sugar groups (deoxyribose in DNA and ribose in RNA), with other types of sugar molecules, otherwise not found in nature.

The same team has since managed to find a way to fold the chain of the artificial XNA molecules to form enzymes. ‘XNAzymes’ showed ‘cut-and-paste’ ability of individual parts of XNA to store and copy genetic or hereditary information, while simultaneously creating and decomposing certain molecules, appropriately.
This ability of XNA, to simultaneously behave as enzymes and to store hereditary information, is considered to be the first promising step towards the creation of artificial life. Next venture would be to make these synthetic molecules reproduce, by replicating themselves, as RNA does.

XNAzymes can be exploited in the development of new therapies that could treat diseases such as cancers and viral infections, since XNAs show extreme robustness compared to DNA. As Dr Holliger points out, XNAs cannot be recognized by our body’s degrading enzymes. They can pass undetected by our organism to deliver drugs and other forms of treatment. Another potential use of XNA-based life-forms could be cleaning the environment of pollutants. A recent study published in Nature by the US National Institute of Health confirmed that environmental contaminants can damage human DNA and cause diseases such as cancer, Alzheimer’s, or diabetes.