Surprising Base Pairing and Structural Properties of 2鈥?Trifluoromethylthio-Modified Ribonucleic Acids

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• 作者：Marija Ko拧uti膰 ; Lukas Jud ; Cyrielle Da Veiga ; Marina Frener ; Katja Fauster ; Christoph Kreutz ; Eric Ennifar ; Ronald Micura
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：May 7, 2014
• 年：2014
• 卷：136
• 期：18
• 页码：6656-6663
• 全文大小：482K
• 年卷期：v.136,no.18(May 7, 2014)
• ISSN：1520-5126

文摘

The chemical synthesis of ribonucleic acids (RNA) with novel chemical modifications is largely driven by the motivation to identify eligible functional probes for the various applications in life sciences. To this end, we have a strong focus on the development of novel fluorinated RNA derivatives that are powerful in NMR spectroscopic analysis of RNA folding and RNA ligand interactions. Here, we report on the synthesis of 2鈥?SCF₃ pyrimidine nucleoside containing oligoribonucleotides and the comprehensive investigation of their structure and base pairing properties. While this modification has a modest impact on thermodynamic stability when it resides in single-stranded regions, it was found to be destabilizing to a surprisingly high extent when located in double helical regions. Our NMR spectroscopic investigations on short single-stranded RNA revealed a strong preference for C2鈥?endo conformation of the 2鈥?SCF₃ ribose unit. Together with a recent computational study (L. Li, J. W. Szostak, J. Am. Chem. Soc. 2014, 136, 2858鈥?865) that estimated the extent of destabilization caused by a single C2鈥?endo nucleotide within a native RNA duplex to amount to 6 kcal mol^鈭? because of disruption of the planar base pair structure, these findings support the notion that the intrinsic preference for C2鈥?endo conformation of 2鈥?SCF₃ nucleosides is most likely responsible for the pronounced destabilization of double helices. Importantly, we were able to crystallize 2鈥?SCF₃ modified RNAs and solved their X-ray structures at atomic resolution. Interestingly, the 2鈥?SCF₃ containing nucleosides that were engaged in distinct mismatch arrangements, but also in a standard Watson鈥揅rick base pair, adopted the same C3鈥?endo ribose conformations as observed in the structure of the unmodified RNA. Likely, strong crystal packing interactions account for this observation. In all structures, the fluorine atoms made surprisingly close contacts to the oxygen atoms of the corresponding pyrimidine nucleobase (O2), and the 2鈥?SCF₃ moieties participated in defined water-bridged hydrogen-bonding networks in the minor groove. All these features allow a rationalization of the structural determinants of the 2鈥?SCF₃ nucleoside modification and correlate them to base pairing properties.