The 3rd Instruct Biennial Structural Biology Meeting, which will take place in Brno, Czech Republic, from May 24 till May 26, 2017. Brno is the city of Johann Gregor Mendel, a founder of modern genetics and one of the first scientists who applied multidisciplinary approach to explain his observations. Social programme of the meeting will include visit of the Mendel’s Museum and dinner at the Augustinian Abbey, where Johann Gregor Mendel worked and lived.
Instruct is a distributed European Research Infrastructure, which provides scientists with access to all major cutting edge technologies that enable biomacromolecular structure determination at atomic resolution. Access to all of these technologies has been available to European member researchers from February 2012. The inaugural Instruct Structural Biology Meeting at Heidelberg in 2013 successfully showcased integrative structural biology and its impact on biological research and biomedicine. The second Biennial took place in Florence in 2015 continuing the integrative line with an increased focus on innovation. This new edition will include sessions that represent recent structural biology highlights, emerging methods and technologies and results of biomedical importance.
The team of Patrick Schultz at the IGBMC has unveiled the architecture of an activated form of RNA polymerase I (RNA Pol I) by cryo electron microscopy. This enzyme synthesizes a particular class of RNA which is necessary for the formation of ribosomes; the molecular machinery responsible for protein synthesis. The results are published in the journal Nature Communications, since July 15th.
RNA Pol I is the enzyme responsible for the synthesis of ribosomal RNAs. The latter can represent up to 80% of the RNA synthesized by a cell. Like the other RNA polymerases, to initiate the ARN synthesis, RNA Pol I must be positioned upstream of the gene to be transcribed on the so-called promoter region thanks to its interaction with specific transcription factors. RNA Pol I transcribes massively one single gene while the type II enzyme is recruited on more than 40,000 different genes whose. Despite many similarities, the modes of action and the control of the two enzymes are therefore very different.
Demonstrate the RNA Pol I binding mode with Rrn3 regulatory factor
To make RNA Pol I transcriptionally competent, it must interact with the protein Rrn3. The team of Patrick Schultz at the IGBMC, in collaboration with the team of Herbert Tschochner from the University of Regensburg in Germany, has analyzed the structure of a complex formed between these two partners. The researchers tried to understand the structural changes responsible for enzyme activation.
The atomic structures of both partners are known by crystallographic studies but the complex remains scarce and is difficult to obtain in vitro because its formation is regulated by a set of post-translational modifications. The German team forced the formation of this complex in yeast by overexpressing Rrn3, the minor partner. The functional complex has been purified in sufficient quantity to be observed by cryo electron microscopy.
Highlight the conformational changes required to activate the enzyme
The published work reveals the 3-D organization of the complex formed between the RNA Pol I and Rrn3 at 0.7 nm spatial resolution. At this level of detail, the secondary structure of both partners is evident allowing the understanding of how they interact with great precision.
Comparison of the new images with the atomic structure of RNA Pol I showed significant differences. The DNA-binding groove adopts a closed position and the N-terminal portion of a subunit of RNA Pol I adopts a radically different position. These changes free the channel used by the triphosphate nucleotides to access the active site of the enzyme.
All these results provide important information about the molecular architecture of the machinery of synthesis of ribosomal RNA.