Structure and functional reselection of the Mango-III fluorogenic RNA aptamer
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| Authors: | Trachman, RJ; Autour, A; Jeng, SCY; Abdolahzadeh, A; Andreoni, A; Cojocaru, R; Garipov, R; Dolgosheina, EV; Knutson, JR; Ryckelynck, M; Unrau, PJ; Ferre-D'Amare, AR |
| Year: | 2019 |
| Journal: | Nat. Chem. Biol. 15: 472-+ Article Link (DOI) PubMed |
| Title: | Structure and functional reselection of the Mango-III fluorogenic RNA aptamer |
| Abstract: | Several turn-on RNA aptamers that activate small-molecule fluorophores have been selected in vitro. Among these, the similar to 30 nucleotide Mango-III is notable because it binds the thiazole orange derivative TO1-Biotin with high affinity and fluoresces brightly (quantum yield 0.55). Uniquely among related aptamers, Mango-III exhibits biphasic thermal melting, characteristic of molecules with tertiary structure. We report crystal structures of TO1-Biotin complexes of Mango-III, a structure-guided mutant Mango-III(A1OU), and a functionally reselected mutant iMango-III. The structures reveal a globular architecture arising from an unprecedented pseudoknot-like connectivity between a G-quadruplex and an embedded non-canonical duplex. The fluorophore is restrained into a planar conformation by the G-quadruplex, a lone, long-range trans Watson-Crick pair (whose A1OU mutation increases quantum yield to 0.66), and a pyrimidine perpendicular to the nucleobase planes of those motifs. The improved iMango-III and Mango-III(A1OU) fluoresce similar to 50% brighter than enhanced green fluorescent protein, making them suitable tags for live cell RNA visualization. |
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