Structural basis of gRNA stabilization and mRNA recognition in trypanosomal RNA editing

Area of Science:

• Molecular Biology
• Parasitology
• Genetics

Background:

• The editosome in Trypanosoma brucei is essential for mitochondrial gene expression, converting cryptic transcripts into functional mRNAs via guide RNA (gRNA)-programmed editing.
• The precise mechanism of information transfer between gRNA and mRNA within the editosome remains poorly understood due to a lack of high-resolution structural data.

Purpose of the Study:

• To elucidate the structural mechanisms underlying gRNA-mRNA interaction and substrate selection by the Trypanosoma brucei editosome.
• To provide high-resolution structural insights into the remodeling events that facilitate RNA editing.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the structures of key editosome subcomplexes.
• Functional studies were conducted to validate the roles of different subcomplexes in RNA binding and editing progression.

Main Results:

• Structures of gRNA-stabilizing RESC-A and gRNA-mRNA-binding RESC-B/RESC-C particles were captured.
• RESC-A sequesters gRNA termini, promoting hairpin formation and blocking mRNA access.
• Conversion of RESC-A to RESC-B/RESC-C facilitates gRNA unfolding and mRNA selection, with the gRNA-mRNA duplex exposed for editing.

Conclusions:

• The study reveals a dynamic remodeling process within the RNA-editing substrate-binding complex (RESC) that is critical for initiating RNA editing.
• This remodeling facilitates gRNA-mRNA hybridization and the assembly of a functional substrate for the RNA-editing catalytic complex (RECC).
• These findings provide a mechanistic basis for how mitochondrial transcripts are recoded into functional mRNAs in Trypanosoma brucei.