A Combined ELONA-(RT)qPCR Approach for Characterizing DNA and RNA Aptamers Selected against PCBP-2

Improvements in Systematic Evolution of Ligands by EXponential enrichment (SELEX) technology and DNA sequencing methods have led to the identification of a large number of active nucleic acid molecules after any aptamer selection experiment. As a result, the search for the fittest aptamers has become a laborious and time-consuming task. Herein, we present an optimized approach for the label-free characterization of DNA and RNA aptamers in parallel. The developed method consists in an Enzyme-Linked OligoNucleotide Assay (ELONA) coupled to either real-time quantitative PCR (qPCR, for DNA aptamers) or reverse transcription qPCR (RTqPCR, for RNA aptamers), which allows the detection of aptamer-target interactions in the high femtomolar range. We have applied this methodology to the affinity analysis of DNA and RNA aptamers selected against the poly(C)-binding protein 2 (PCBP-2). In addition, we have used ELONA-(RT)qPCR to quantify the dissociation constant (Kd) and maximum binding capacity (Bmax) of 16 high affinity DNA and RNA aptamers. The Kd values of the high affinity DNA aptamers were compared to those derived from colorimetric ELONA performed in parallel. Additionally, Electrophoretic Mobility Shift Assays (EMSA) were used to confirm the binding of representative PCBP-2-specific RNA aptamers in solution. We propose this ELONA-(RT)qPCR approach as a general strategy for aptamer characterization, with a broad applicability in biotechnology and biomedicine.This work was supported by the Spanish Ministerio de Economía y Competitividad (MINECO: grants RTC-2014-1986-1 and BIO2016-79618-R—funded by EU under the FEDER programme—to C.B., and BIO2015-72716-EXP and BFU2017-84492-R to E.M.S.) as well as by an institutional grant from Fundación Ramón Areces. CIBERehd is funded by the Instituto de Salud Carlos III (ISCIII)We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI