The Lin28 cold-shock domain remodels pre-let-7 microRNA |
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Authors: | Mayr Florian Schütz Anja Döge Nadine Heinemann Udo |
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Institution: | 1Crystallography, Max-Delbrück Center for Molecular Medicine, Robert-Rössle Straße 10, 13125, 2Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 and 3Helmholtz-Protein Sample Production Facility, Max-Delbrück Center for Molecular Medicine, Robert-Rössle Straße 10, 13125 Berlin, Germany |
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Abstract: | The RNA-binding protein Lin28 regulates the processing of a developmentally important group of microRNAs, the let-7 family. Lin28 blocks the biogenesis of let-7 in embryonic stem cells and thereby prevents differentiation. It was shown that both RNA-binding domains (RBDs) of this protein, the cold-shock domain (CSD) and the zinc-knuckle domain (ZKD) are indispensable for pri- or pre-let-7 binding and blocking its maturation. Here, we systematically examined the nucleic acid-binding preferences of the Lin28 RBDs and determined the crystal structure of the Lin28 CSD in the absence and presence of nucleic acids. Both RNA-binding domains bind to single-stranded nucleic acids with the ZKD mediating specific binding to a conserved GGAG motif and the CSD showing only limited sequence specificity. However, only the isolated Lin28 CSD, but not the ZKD, can bind with a reasonable affinity to pre-let-7 and thus is able to remodel the terminal loop of pre-let-7 including the Dicer cleavage site. Further mutagenesis studies reveal that the Lin28 CSD induces a conformational change in the terminal loop of pre-let-7 and thereby facilitates a subsequent specific binding of the Lin28 ZKD to the conserved GGAG motif. |
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