Summary: Steric exclusion is a key element of enzyme substrate specificity, including in polymerases. Such substrate specificity restricts the enzymatic synthesis of 2'-modified nucleic acids, which are of interest in nucleic acid-based drug development. Here we describe the discovery of a two-residue, nascent strand, steric control "gate" in an archaeal DNA polymerase. We show that engineering of the gate to reduce steric bulk in the context of a previously-described RNA polymerase activity unlocks the synthesis of 2'-modified RNA oligomers, specifically the efficient synthesis of both defined and random-sequence 2'-O-methyl-RNA (2'OMe-RNA) and 2'-O-(2-methoxyethyl)-RNA (MOE-RNA) oligomers up to 750 nt. This enabled the discovery of RNA endonuclease catalysts entirely composed of 2'OMe-RNA ("2'OMezymes") for the allele-specific cleavage of oncogenic KRAS (G12D) and β-catenin CTNNB1 (S33Y) mRNAs, and the elaboration of mixed 2'OMe- / MOE-RNA aptamers with high affinity for Vascular Endothelial Growth Factor. Our results open up these 2'-modified RNAs-used in several approved nucleic acid therapeutics-for enzymatic synthesis and a wider exploration in directed evolution and nanotechnology.
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Steric exclusion is a key element of enzyme substrate specificity, including in polymerases. Such substrate specificity restricts the enzymatic synthesis of 2'-modified nucleic acids, which are of interest in nucleic acid-based drug development. Here we describe the discovery of a two-residue, nascent strand, steric control "gate" in an archaeal DNA polymerase. We show that engineering of the gate to reduce steric bulk in the context of a previously-described RNA polymerase activity unlocks the synthesis of 2'-modified RNA oligomers, specifically the efficient synthesis of both defined and random-sequence 2'-O-methyl-RNA (2'OMe-RNA) and 2'-O-(2-methoxyethyl)-RNA (MOE-RNA) oligomers up to 750 nt. This enabled the discovery of RNA endonuclease catalysts entirely composed of 2'OMe-RNA ("2'OMezymes") for the allele-specific cleavage of oncogenic KRAS (G12D) and β-catenin CTNNB1 (S33Y) mRNAs, and the elaboration of mixed 2'OMe- / MOE-RNA aptamers with high affinity for Vascular Endothelial Growth Factor. Our results open up these 2'-modified RNAs-used in several approved nucleic acid therapeutics-for enzymatic synthesis and a wider exploration in directed evolution and nanotechnology.
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