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| Quality control during splicing: When an error in the precursor mRNA is detected, the spliceosome is blocked, the recruited control factors interrupt the “normal” cycle, and a molecular short circuit causes the spliceosome to disassemble. Image Credit: © K. Wild, K. Soni, I. Sinning |
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Researchers successfully visualized a "blocked" spliceosome at high resolution for the first time, revealing the specific mechanism by which cells detect and discard errors during the mRNA splicing process.
- Methodology: The team utilized cryo-electron microscopy to examine defective spliceosomes purified from the fission yeast Schizosaccharomyces pombe, employing molecular markers to isolate the specific complexes stalled by quality control factors.
- Key Data: The study produced the first atomic-level representation of a discarded spliceosome, demonstrating that a "molecular short circuit" occurs upon error detection to trigger the immediate disassembly of the faulty complex.
- Significance: Elucidating this quality control mechanism is critical for medical science, as splicing errors are a primary cause of hereditary genetic disorders and are strongly associated with neurodevelopmental conditions and cancer.
- Future Application: These detailed structural models provide a foundational blueprint for analyzing molecular malfunctions in splicing-related diseases, which may facilitate the development of targeted therapies for conditions caused by aberrant gene expression.
- Branch of Science: Biochemistry and Molecular Biology.
- Additional Detail: The proteins responsible for this quality control process are conserved from fission yeast to humans, indicating that this error-correction mechanism has remained evolutionarily stable and fundamental to eukaryotic life
A complex molecular machine, the spliceosome, ensures that the genetic information from the genome, after being transcribed into mRNA precursors, is correctly assembled into mature mRNA. Splicing is a basic requirement for producing proteins that fulfill an organism’s vital functions. Faulty functioning of a spliceosome can lead to a variety of serious diseases. Researchers at the Heidelberg University Biochemistry Center (BZH) have succeeded for the first time in depicting a faultily “blocked” spliceosome at high resolution and reconstructing how it is recognized and eliminated in the cell. The research was conducted in collaboration with colleagues from the Australian National University.
The genetic information of all living organisms is contained in the DNA, with the majority of genes in higher organisms being structured in a mosaic-like manner. So the cells are able to “read” the instructions for building proteins stored in these genetic mosaic particles, they are first copied into precursors of mRNA, or messenger RNA. The spliceosome then converts them into mature, functional mRNA. To do this, this large protein-RNA complex, which is located in the cell nucleus, removes non-coding sections (introns) from mRNA precursors and links the coding sections (exons) to form a continuous strand of information. Errors in this process, also known as splicing, are one of the main causes of inheritable genetic disorders and are associated with neurodevelopmental disorders and diseases such as cancer. It was known that the spliceosome has quality control mechanisms, but the mechanistic details were not understood.
For their experiments, the Heidelberg researchers led by BZH director Prof. Dr Irmgard Sinning used the fission yeast Schizosaccharomyces pombe, a model organism frequently used in cell biology. Using molecular markers, defective spliceosomes were identified, purified, and structurally examined via cryo-electron microscopy. “The largely stable structure of the spliceosome center enabled us to obtain high-resolution information. This means that a spliceosome discarded during cellular quality control can be represented at the atomic level for the first time,” states the structural biologist. “However, analyzing the components flexibly bound to the periphery of the spliceosome was a major challenge for our work,” explains Dr Komal Soni from the BZH.
Based on this structural information, the scientists were able to understand which errors occur during splicing, how the spliceosome recognizes faulty processes and subsequently aborts the splicing, thereby sorting out the faulty complex. Using the detailed structures, the researchers were also able to model the underlying molecular mechanisms. The proteins involved in this process of cellular quality control are conserved in eukaryotic organisms from fission yeast to humans. The scientists therefore assume that the mechanisms for recognizing and sorting out faulty spliceosomes have remained largely unchanged over the course of evolution.
The research was carried out as part of a long-term collaboration between the teams of Prof. Sinning and Prof. Dr Tamas Fischer, who specializes in RNA surveillance at the Australian National University in Canberra. Prof. Dr Henning Urlaub’s research group at the Max Planck Institute for Multidisciplinary Sciences in Göttingen also participated.
Funding: The work was funded by the German Research Foundation and the Australian Research Council.
Published in journal: Nature Structural & Molecular Biology
Title: Structures of aberrant spliceosome intermediates on their way to disassembly
Authors: Komal Soni, Attila Horvath, Olexandr Dybkov, Merlin Schwan, Sasanan Trakansuebkul, Dirk Flemming, Klemens Wild, Henning Urlaub, Tamás Fischer, and Irmgard Sinning
Source/Credit: Heidelberg University
Reference Number: bmol020725_01