Surface-driven RNA-refolding by the OB-fold proteins of the Trypanosoma brucei editosome

RNA editing in African trypanosomes represents an RNA-processing reaction that generates functional mitochondrial transcripts from sequence-deficient pre-mRNAs. The reaction is catalyzed by a macromolecular protein complex known as the editosome. Editosomes have been demonstrated to execute RNA-chaperone activity to overcome the highly folded nature of pre-edited substrate mRNAs. The molecular basis of this activity is unknown. Here we test five OB-fold proteins of the editosome as potential candidates. We show that the different proteins interact by hetero-oligomerization and we demonstrate that all proteins execute RNA-chaperone activity. Activity differences correlate with the surface areas of the proteins and map predominantly to the intrinsically disordered subdomains of the polypeptides. To provide a structural context for our findings we present a coarse-grained model of the editosome. The model suggests that an inner core of catalytically active editosome components is separated from an outer shell of IDP-domains that act as RNA-remodeling sites.