The largest yeast protein decoded at the atomic level
Dec. 4, 2018
Ribosomes play an essential role in living things: they are the central sources of protein production in all types of cells. In eukaryotes, the assembly and maturation of these gigantic protein factories are initiated in the cell nucleus by various factors, including Rea1, which is the largest and most complex yeast protein. Thanks to cryoelectron microscopy, Helgo Schmidt's team at the IGBMC (CNRS/Inserm/University of Strasbourg) unveils the fine structure of the maturation factor Rea1. Published on 21 November 2018 in the journal eLife, this work makes it possible to visualize at the atomic scale one of the major mechanisms of ribosome maturation.
Real molecular machines, ribosomes decipher the information contained in a copy of DNA, called messenger RNA, to synthesize proteins. But how are ribosomes themselves produced? Their assembly is initiated in the nucleus where the proteins and RNAs constituting the large ribosomal subunit interact with more than 200 assembly factors. Ultimately, the large mature subunit is found in the cellular cytoplasm where it joins the small ribosomal subunit to form functional ribosomes. In order to promote the export of the large subunit from the nucleus to the cytoplasm, the Rea1 protein eliminates some of the assembly factors.
Rea1 is a huge protein of 5000 amino acids, which consists of a ring and a tail. At the ring level, the hydrolysis of ATP occurs, which allows the release of energy. This mechanism triggers a remodeling process in the tail, which in turn generates a mechanical force to eliminate assembly factors. Despite the crucial importance of ribosome maturation, the fine structure and mechanism of Rea1 remained largely enigmatic.
Using cryoelectron microscopy, the researchers were able to construct a detailed atomic model of Rea1, which revealed that an "arm" associated with the center of the ring regulates the hydrolysis of ATP. The "arm" also controls the formation of a binding site that allows Rea1 to interact with the assembly factors it must eliminate. In addition, the model revealed large portions of the tail of Rea1 and provided insights into a key question, namely how hydrolysis of ATP in the ring could cause tail remodeling.
All these results provide important information on the molecular architecture of the largest ribosome maturation factor.
This study was funded by a LabEx Chair (LabEx INRT),an ATIP-Avenir grant as well as a Région Grand Est jeunes chercheurs fellowship.