Naturehttp://doi.org/xwd(2014)

Xeno-nucleic acids (XNAs) are synthetic genetic polymers containing non-natural components such as alternative nucleobases, sugars, or a connecting backbone with a different chemical structure. This introduction of a wider selection of functional building blocks could enable XNA sequences to participate in a wider selection of chemical reactions than their DNA or RNA equivalents. However, although XNAs have previously been shown to bind ligands and fold into defined structures, little was known about their ability to catalyse chemical reactions.

A team led by Philipp Holliger at the MRC Laboratory of Molecular Biology, Cambridge, UK, has now created a series of XNA sequences — which they call XNAzymes — that can act as catalysts. The XNAzymes were created using nucleic acid sequences in which the normal ribofuranose ring found in DNA and RNA was replaced with a synthetic analogue. Using four different sugars enabled the fabrication of XNAzymes based on four different types of XNA: arabino nucleic acids (ANA); 2′-fluoroarabino nucleic acids (FANA); hexitol nucleic acids (HNA); and cyclohexene nucleic acids (CeNA). To identify XNA sequences that could catalyse reactions, the team employed previously developed techniques for replicating and selecting XNA sequences. This led to the development of XNAzymes that could cleave a phosphodiester bond in RNA. XNAzymes from each of the four different types of XNA were shown to possess this RNA endonuclease-like activity.

A similar series of experiments using a different selection strategy identified XNAzymes that could act as RNA ligases by joining two RNA strands. Next, the team investigated whether XNAzymes with ligase activity could join two XNA strands. By carefully selecting both the XNAzyme and the XNA substrates, the team demonstrated that XNAzymes could repeatedly catalyse the iterative addition of short XNA substrates to form longer XNA oligomers of up to 100 nucleotides in length. In a final demonstration, an XNAzyme with ligase activity was shown to be capable of catalysing the formation of an XNAzyme with RNA endonuclease activity. These examples showed that XNA sequences can form a fully synthetic catalytic system.