2′-Fluoro-arabinonucleic Acid (FANA): A Versatile Tool for Probing Biomolecular Interactions

CONSPECTUS: This Account highlights the structural features that render 2'-deoxy-2'-fluoro-arabinonucleic acid (FANA) an ideal tool for mimicking DNA secondary structures and probing biomolecular interactions relevant to chemical biology. The high binding affinity of FANA to DNA and RNA has had implications in therapeutics. FANA can hybridize to complementary RNA, resulting in a predominant A-form helix stabilized by a network of 2'F-H8(purine) pseudohydrogen bonding interactions. We have shown that FANA/RNA hybrids are substrates of RNase H and Ago2, both implicated in the mechanism of action of antisense oligonucleotides (ASOs) and siRNA, respectvely. This knowledge has helped us study the conformational preferences of ASOs and siRNA as well as crRNA in CRISPR-associated Cas9, thereby revealing structural features crucial to biochemical activity. Additionally, FANA is of particular use in stabilizing noncanonical DNA structures. For instance, we have taken advantage of the anti N-glycosidic bond conformation of FANA monomers to induce a parallel topology in telomeric G-quadruplexes. Subsequent singlemolecule FRET studies elucidated the mechanism by which these parallel G-quadruplexes are recognized and extended by telomerase. Similarly, we have utilized FANA to stabilize elusive telomeric i-motifs in the presence of concomitant parallel Gquadruplexes and under physiological conditions, thereby reinforcing their potential relevance to telomere biology. In another study, we adapted microarray technology and used FANA substitutions to enhance the binding affinity of the G-quadruplex thrombinbinding aptamer to its thrombin target. Finally, we discovered that DNA polymerases can synthesize FANA strands from DNA templates. On the basis of this property, other groups demonstrated that FANA, like DNA, can store hereditary information. They did so by engineering polymerases to efficiently transfer genetic information from DNA to FANA and retrieve it back into DNA. Subsequent studies showed that FANA could be evolved to acquire ribozyme-like endonuclease or ligase activity and to form high-affinity aptamers. Overall, the implications of these studies are remarkable because they promise a deeper understanding of human biochemistry for innovative therapeutic avenues. This Account summarizes past achievements and provides an outlook for inspiring the increased use of FANA in biological applications and fostering interdisciplinary collaborations.