Design and Characterization of Aptamers to Antibiotic Kanamycin with Improved Affinity

Aptamers are promising synthetic molecular receptors that bind to specific targets by adopting a unique tertiary structure. However, their selection using standard SELEX protocols often does not allow the achievement of high affinity to the targets. Due to the lack and difficulty of obtaining data on the 3D structure of aptamers and their complexes, the design of known aptamers based on simple rules and software is in demand. The presented work considers the comparative characterization and design of DNA aptamers specific to the antibiotic kanamycin based on complementary interactions and structural motifs (bulges, mismatches, loops) predicted by NUPACK, RNAfold, and UNAFold software. The design included the elimination of non-functional parts of the aptamers and the stabilization of the kanamycin-binding loop. Seven novel aptamers, chosen based on these predictions, were synthesized, and their affinities were measured using an isothermal titration calorimetry technique. The prediction of end stem and hairpin loop structures was confirmed by comparison with circular dichroism data. As a result of sequential design with truncation of unnecessary nucleotides, a novel optimal 42-base-long aptamer was designed and demonstrated a dissociation constant of 109 ± 15 nM, which is 4.7-fold lower than the initial preparation (470 ± 40 nM) and overcomes all known aptamers to kanamycin.