Poster abstracts
Poster number 152 submitted by Sarah Starcovic
Structure Validation of a Group II Intron RNA Dimer using Small-Angle X-ray Scattering
Sarah Starcovic (Department of Biochemistry and Molecular Medicine, West Virginia University), Aaron Robart (Department of Biochemistry and Molecular Medicine, West Virginia University)
Abstract:
Group II introns are catalytic RNAs (ribozymes) that mediate self-splicing through two competing pathways: a non-physiological hydrolytic reaction and a branched splicing reaction that produces intron lariats. Many group II introns encode an intron-encoded protein (IEP) that enhances splicing efficiency. A primitive subtype, known as IIC introns, depends on the IEP for efficient lariat formation. This mechanism closely resembles the splicing reaction carried out by the eukaryotic spliceosome, highlighting the evolutionary relationship between these systems. Because of their ribonucleoprotein (RNP)-dependent activity, IIC introns provide a powerful model for investigating the evolutionary transition from self-splicing ribozymes to the complex RNP-based splicing machinery found in eukaryotic cells. They also offer insight into the structural and functional interplay between RNA and protein during catalysis. Here, we present cryo-electron microscopy (cryo-EM) reconstructions of a dimeric group II intron RNA and its corresponding RNP complex. Using small-angle X-ray scattering (SAXS), we confirm the dimeric state in solution and distinguish it from a monomeric mutant at equilibrium. Notably, the dimer persists upon addition of the IEP. This SAXS data showcases a novel application of the method to large RNA-only and RNP complexes, expanding our knowledge of RNA-protein interactions and the dynamic nature of RNA. This data expands the currently limited repertoire of RNP models and provides new insights into how proteins stabilize and modulate RNA catalytic function. Additionally, we present evidence for a SAXS-based approach to characterize very large RNP assemblies and validate cryo-EM observations, which may be broadly applicable to other macromolecular systems.
Keywords: ribozymes, CryoEM, SAXS