LAUSR

RNA or single-stranded DNA aptamers with 2'-F pyrimidines have been pursued to increase resistance to nucleases, and while it seems likely that these and other modifications, including the modification of purines, could be used to optimize additional properties, this has been much less explored because such aptamers are challenging to discover. Using a thermostable DNA polymerase, SFM4-3, which was previously evolved to accept nucleotides with 2'-modifications, we now report the selection of 2'-F purine aptamers that bind human neutrophil elastase (HNE). Two aptamers were identified, 2fHNE-1 and 2fHNE-2, that bind HNE with reasonable affinity. Interestingly, the 2'-F substituents facilitate the selection of specific interactions with HNE and overcome nonspecific electrostatic interactions that can otherwise dominate. The data demonstrate that inclusion of only a few 2'-F substituents can optimize properties far beyond simple nuclease resistance and that SFM4-3 should prove valuable for the further exploration and production of aptamers with properties optimized for various applications.