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Acta Crystallogr F Struct Biol Commun. 2019 Aug 1;75(Pt 8):547-551. doi: 10.1107/S2053230X19010136. Epub 2019 Aug 2.

Co-crystal structure of the iMango-III fluorescent RNA aptamer using an X-ray free-electron laser.

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Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, Bethesda, Maryland, USA.
Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, Maryland, USA.
Center for Free Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany.


Turn-on aptamers are in vitro-selected RNAs that bind to conditionally fluorescent small molecules and enhance their fluorescence. Upon binding TO1-biotin, the iMango-III aptamer achieves the largest fluorescence enhancement reported for turn-on aptamers (over 5000-fold). This aptamer was generated by structure-guided engineering and functional reselection of the parental aptamer Mango-III. Structures of both Mango-III and iMango-III have previously been determined by conventional cryocrystallography using synchrotron X-radiation. Using an X-ray free-electron laser (XFEL), the room-temperature iMango-III-TO1-biotin co-crystal structure has now been determined at 3.0 Å resolution. This structural model, which was refined against a data set of ∼1300 diffraction images (each from a single crystal), is largely consistent with the structures determined from single-crystal data sets collected at 100 K. This constitutes a technical benchmark on the way to XFEL pump-probe experiments on fluorescent RNA-small molecule complexes.


RNA structure; X-ray free-electron lasers; XFELS; fluorescence; fluorescence turn-on aptamers; iMango-III; room temperature

[Available on 2020-08-01]

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