A Small Cyclic β-Hairpin Peptide Mimics the Rbfox2 RNA Recognition Motif and Binds to the Precursor miRNA 20b.

The RNA recognition motif (RRM), which is the most abundant RNA-binding motif in eukaryotes, is a well-structured domain of about 90 amino acids, yet the β2β3 hairpin, corresponding to strands 2 and 3 of the β-sheet, and the intervening loop make essential interactions with RNA in many RRM complexes. A series of small cyclic peptide mimics of the β2β3 hairpin of Rbfox2 protein that recognize the terminal loop of precursor miR-20b have been designed to investigate whether the full RNA-binding protein can be mimicked with a minimal structurally preorganized peptide. Within a small library of seven cyclic peptides, a peptide with low-micromolar affinity for the miR-20b precursor was found. NMR spectroscopy titration data suggest that this peptide specifically targets the apical loop of pre-miR-20b. This work shows that it is possible to mimic RNA-binding proteins with designed stable peptides, which provide a starting point for designing or evolving small peptide mimetics of RRM proteins.