DNA nanotechnology has created nanostructures with astonishing complexity. However, with nanostructures becoming increasingly larger and more intricate, they have become more difficult to obtain in high yields and quality. Expanding the alphabet beyond the canonical base pairs can therefore be the key to push the technology to the next level. Here, we describe examples of DNA nanostructures built from an “anthropogenic evolvable genetic information system (AEGIS).” Because AEGIS uses the same backbone as DNA, the existing rules for designing DNA nanostructures can be readily applied to AEGIS nanostructures, which also show greater stability, both thermal and enzymatic, greater control over autonomous assembly, and good phase separation. AEGIS can have as many as 12 different units and six different pairs with Watson-Crick-Franklin geometry. Thus, if further developed, then these nanostructures may represent a previously unexplored frontier in DNA nanoscience and nanotechnology, expanding the space of “soft” biomaterial design.

ALternative Isoinformational ENgineered” (ALIEN) DNA is a biomimetic polymer composed of four entirely anthropogenic nucleotides. These alternative nucleosides form base pairs orthogonal to canonical bases and fold into the familiar B-form DNA double-helix, endowing ALIEN DNA with valuable biotechnological applications. The ability to sequence ALIEN DNA is essential for its continued development. However traditional sequencing approaches rely on chemical recognition of ACGT-DNA and cannot be easily adapted to ALIEN DNA. Here we demonstrate de novo nanopore sequencing of DNA comprised entirely of the four anthropogenic DNA bases. We show direct, label-free, single-molecule sequencing of such nucleic acids without the requirements of fluorescent labels, transliteration, amplification, or enzymatic synthesis. This paves the way for routine, accessible, and high-accuracy sequencing of DNA beyond A, C, G, and T.

Adding synthetic nucleotides to DNA increases the linear information density of DNA molecules. Here we report that it also can increase the diversity of their three-dimensional folds. Specifically, an additional nucleotide (dZ, with a 5-nitro-6-aminopyridone nucleobase), placed at twelve sites in a 23-nucleotides-long DNA strand, creates a fairly stable unimolecular structure (that is, the folded Z-motif, or fZ-motif) that melts at 66.5°C at pH 8.5. Spectroscopic, gel and two-dimensional NMR analyses show that the folded Z-motif is held together by six reverse skinny dZ^-:dZ base pairs, analogous to the crystal structure of the free heterocycle. Fluorescence tagging shows that the dZ^-:dZ pairs join parallel strands in a four-stranded compact down-up-down-up fold. These have two possible structures: one with intercalated dZ^-:dZ base pairs, the second without intercalation. The intercalated structure would resemble the i-motif formed by dC:dC⁺-reversed pairing at pH ≤ 6.5. This fZ-motif may therefore help DNA form compact structures needed for binding and catalysis.

The ability of nucleic acids to catalyze reactions (as well as store and transmit information) is important for both basic and applied science, the first in the context of molecular evolution and the origin of life and the second for biomedical applications. However, the catalytic power of standard nucleic acids (NAs) assembled from just four nucleotide building blocks is limited when compared with that of proteins. Here, we assess the evolutionary potential of libraries of nucleic acids with six nucleotide building blocks as reservoirs for catalysis. We compare the outcomes of in vitro selection experiments toward RNA-cleavage activity of two nucleic acid libraries: one built from the standard four independently replicable nucleotides and the other from six, with the two added nucleotides coming from an artificially expanded genetic information system (AEGIS). Results from comparative experiments suggest that DNA libraries with increased chemical diversity, higher information density, and larger searchable sequence spaces are one order of magnitude richer reservoirs of molecules that catalyze the cleavage of a phosphodiester bond in RNA than DNA libraries built from a standard four-nucleotide alphabet. Evolved AEGISzymes with nitro-carrying nucleobase Z appear to exploit a general acid–base catalytic mechanism to cleave that bond, analogous to the mechanism of the ribonuclease A family of protein enzymes and heavily modified DNAzymes. The AEGISzyme described here represents a new type of catalysts evolved from libraries built from expanded genetic alphabets.