Exploring the suitability of RanBP2-type Zinc Fingers for RNA-binding protein design

Transcriptomes consist of several classes of RNA that have wide-ranging but often poorly described functions and the deregulation of which leads to numerous diseases. Engineering of functionalized RNA-binding proteins (RBPs) could therefore have many applications. Our previous studies suggested that the RanBP2-type Zinc Finger (ZF) domain is a suitable scaffold to investigate the design of single-stranded RBPs. In the present work, we have analyzed the natural sequence specificity of various members of the RanBP2-type ZF family and characterized the interaction with their target RNA. Surprisingly, our data showed that natural RanBP2-type ZFs with different RNA-binding residues exhibit a similar sequence specificity and therefore no simple recognition code can be established. Despite this finding, different discriminative abilities were observed within the family. In addition, in order to target a long RNA sequence and therefore gain in specificity, we generated a 6-ZF array by combining ZFs from the RanBP2-type family but also from different families, in an effort to achieve a wider target sequence repertoire. We showed that this chimeric protein recognizes its target sequence (20 nucleotides), both in vitro and in living cells. Altogether, our results indicate that the use of ZFs in RBP design remains attractive even though engineering of specificity changes is challenging.