Our work suggests that the tryptophan cage motif plays a structural role, rather than in RNA recognition. An NMR structural ensemble of the hnRNPR-like protein DND1 eRRM1-RRM2 domains bound to RNA (PDB ID 7Q4L), solved by the Allain group, showed that this region does not contact RNA:

Finally, we compare to previously solved structures of hnRNPR-like proteins hnRNPRQ and DND1 to identify common features in the eRRM motif.

To see if these residues are biologically significant, we surveyed the COSMIC database and found several cancer-associated missense mutations in the tryptophan cage motif and residues in the Next-RRM interface:

Alanine substitution of residues in the Next-RRM interface or tryptophan cage reduce thermal stability and increase conformational dynamics, indicating an important role in protein folding:

The intervening loop is highly conserved and contains a tryptophan cage, previously reported in the synthetic tryptophan cage (Trp-cage) peptide. To our knowledge, this is the first time a tryptophan cage has been reported in a naturally occurring protein.

The Next and RRM are held together by a highly charged interface, hydrophobic contacts, and hydrogen bonds:

Happy to share our latest work! Here, we solved the X-ray crystal structure of the hnRNPR RRM1 (our group’s first structure!). We identified an extended RRM (eRRM), where a 45-aa N-terminal extension (Next) motif docks to the RRM:

www.biorxiv.org/content/10.1...

Had fun tonight fishing crystals for an upcoming synchrotron trip! A bit late for #FluorescenceFriday, but is a first for us to work with fluorescent crystals 😎

Hi! I am a biophysical chemist & Assistant Professor at UNL passionate about all things #NMR and #RNA. I lead a research team that uses structural, biochemical+biophysical, and cellular tools to understand how RNA folding and macromolecular assembly impacts human health and disease.