CLICK-17, a DNA enzyme that harnesses ultra-low concentrations of either Cu(+) or Cu(2+) to catalyze the azide-alkyne ‘click’ reaction in water

To enable the optimal, biocompatible and non-destructive application of the highly useful copper (Cu(+))-mediated alkyne-azide ‘click’ cycloaddition in water, we have isolated and characterized a 79-nucleotide DNA enzyme or DNAzyme, ‘CLICK-17’, that harnesses as low as sub-micromolar Cu(+); or, surprisingly, Cu(2+) (without added reductants such as ascorbate) to catalyze conjugation between a variety of alkyne and azide substrates, including small molecules, proteins and nucleic acids. CLICK-17’s Cu(+) catalysis is orders of magnitude faster than that of either Cu(+) alone or of Cu(+) complexed to PERMUT-17, a sequence-permuted DNA isomer of CLICK-17. With the less toxic Cu(2+), CLICK-17 attains rates comparable to Cu(+), under conditions where both Cu(2+) alone and Cu(2+) complexed with a classic accelerating ligand, THPTA, are wholly inactive. Cyclic voltammetry shows that CLICK-17, unlike PERMUT-17, powerfully perturbs the Cu(II)/Cu(I) redox potential. CLICK-17 thus provides a unique, DNA-derived ligand environment for catalytic copper within its active site. As a bona fide Cu(2+)-driven enzyme, with potential for being evolved to accept only designated substrates, CLICK-17 and future variants promise the fast, safe, and substrate-specific catalysis of ‘click’ bioconjugations, potentially on the surfaces of living cells.