Simultaneous Generation of Aptamers to Multiple Gamma-Carboxyglutamic Acid Proteins from a Focused Aptamer Library Using DeSELEX and Convergent Selection

By using the in vitro selection method SELEX against the complex mixture of GLA proteins and utilizing methods to deconvolute the resulting ligands, we were able to successfully generate 2′-ribo purine, 2′-fluoro pyrimidine aptamers to various individual targets in the GLA protein proteome that ranged in concentration from 10 nM to 1.4 μM in plasma. Perhaps not unexpectedly, the majority of the aptamers isolated following SELEX bind the most abundant protein in the mixture, prothrombin (FII), with high affinity. We show that by deselecting the dominant prothrombin aptamer the selection can be redirected. By using this DeSELEX approach, we were able to shift the selection toward other sequences and to less abundant protein targets and obtained an aptamer to Factor IX (FIX). We also demonstrate that by using an RNA library that is focused around a proteome, purified protein targets can then be used to rapidly generate aptamers to the protein targets that are rare in the initial mixture such as Factor VII (FVII) and Factor X (FX). Moreover, for all four proteins targeted (FII, FVII, FIX, and FX), aptamers were identified that could inhibit the individual protein's activitity in coagulation assays. Thus, by applying the concepts of DeSELEX and focused library selection, aptamers specific for any protein in a particular proteome can theoretically be generated, even when the proteins in the mixture are present at very different concentrations.