Polymerase Evolution Enables Access to Glycosylated Xeno-Nucleic Acids with Expanded Chemical Functionality

Chemical modifications expand the functional repertoire of nucleic acids, but the extent to which complex glycans can be integrated into genetic polymers remains largely unexplored. Glycosylated nucleic acids, including glycoRNAs and bacteriophage genomes, are emerging as key mediators of host-pathogen interactions, yet their synthetic accessibility is severely limited by the inability of polymerases to process substrates bearing simultaneous base and backbone modifications. Here we report the directed evolution of a family B DNA polymerase that enables the synthesis of glycosylated xeno-nucleic acids (XNAs). Using fluorescence-activated droplet sorting, we identified an engineered polymerase, termed G2, that efficiently incorporates nucleotides bearing mono- to trisaccharide base-appendages together with C2 substitutions, yielding XNAs containing up to 30% glycosylated bases. Deep sequencing of >93,000 chimeras reveals that this activity arises from epistatic networks concentrated within catalytic domains. These results establish a route to glycan-encoded nucleic acids and advance polymerase engineering for chemically expanded therapeutics.