Exon and protein positioning in a pre-catalytic group II intron RNP primed for splicing

Area of Science:

• Molecular Biology
• Structural Biology
• RNA Biology

Background:

• Group II introns are RNA-based catalysts and evolutionary precursors to nuclear spliceosomal introns.
• They utilize a conserved two-step splicing mechanism involving a ribonucleoprotein (RNP) complex.
• Previous structural studies lacked pre-catalytic models, hindering understanding of the splicing mechanism.

Purpose of the Study:

• To elucidate the structural basis of group II intron splicing by obtaining cryo-EM structures of pre-catalytic RNPs.
• To identify structural rearrangements associated with the catalytic activation and splicing process.
• To compare pre-catalytic and spliced states to understand RNA-protein interactions during splicing.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine high-resolution structures.
• Analysis of endogenously produced group II intron RNPs.
• Comparative structural analysis of pre-catalytic and spliced intron RNP complexes.

Main Results:

• Two cryo-EM structures of group II intron RNPs in the pre-catalytic state were determined.
• Key structural rearrangements, including active site remodeling and exon engagement, were identified upon splicing.
• Altered RNA-protein interactions and the impact of active site formation on RNP architecture were revealed.

Conclusions:

• The study provides crucial structural insights into IEP-assisted group II intron splicing.
• Findings fill a significant gap in understanding the dynamic structural changes during intron splicing.
• The results offer parallels to the evolutionarily related spliceosomal splicing mechanism.