Structure and function of ribonucleoprotein complexes assembly factors involved in human pathologies. – RNPgenesis

Our goal is to contribute to the understanding of the biogenesis of molecular complexes using structural biology to determine the structure of proteins involved in the assembly of these complexes. Based on our preliminary results, we targeted several different aspects of the maturation of ribonucleoprotein particles (RNP) for which structural studies can be considered. The project will focus on protein complexes that are either small autonomous complexes that are recruited en bloc by the RNP or complexes that form inside the RNP during the assembly. We will address such protein-RNA complexes, when the site of RNA binding is known. The determined structures will lead to functional hypotheses that are then tested in vivo in the yeast model system.

The structure of a protein-protein complex by X-ray crystallography was solved early in the project. This allowed us to understand for the first time how a protein important in the process of biogenesis of molecular complexes functions. Other complexes have been reconstituted and their analysis is in progress.

The structure of a protein-protein complex by X-ray crystallography was solved early in the project. This allowed us to understand for the first time how a protein important in the process of biogenesis of molecular complexes. Other complexes have been reconstituted and their analysis is in progress.

Two publications in preparation

Ribonucleoproteins (RNPs) are complexes composed of proteins and RNA molecules that plain crucial roles in the cell. These RNPs are involved in a wide range of cellular and biochemical functions, from maturation of different classes of RNAs to protein synthesis, and represent some of the most complicated molecular machines. Our interest lies in understanding how these molecular machines are assembled and regulated in the cell. In eukaryotes, the ribosome cannot assemble spontaneously and its biogenesis requires the coordinated action of more than 200 non ribosomal proteins starting in a specialized compartment called the nucleolus and ending in the cytoplasm, in an extremely regulated process in time and space. Even a “simple” RNP such as snoRNPs (Small Nucleolar RNPs), composed of four proteins and one RNA, undergoes a complex maturation process.

The precise function of these RNPs is often essential, and any deregulation generally has dramatic consequences for cell fate. Our project focuses on RNP assembly factors involved in human pathologies, and embrace different RNPs such as the ribosome, telomerase, snoRNPs and the spliceosome. Mutations in proteins involved in ribosome biogenesis have been recognized as a major cause of rare genetics disorders such as Diamond-Blackfan anemia, Shwachman-Diamond syndrome, dyskeratosis congenita, cartilage hair hypoplasia, Treacher-Collins Syndrome and 5q- syndrome. The p53 surveillance pathway is also activated by defects in ribosome biogenesis, indicating that disruptions in translation control may lead to cancer predisposition. Telomerase is activated in 80% of cancers, and its action is necessary for the infinite replicative life span of cancerous cells. Factors involved in the biogenesis of telomerase represent attractive targets for inhibiting telomerase.

Although a large number of factors have been identified in the regulation and biogenesis of various RNPs, the precise function of the majority of these proteins remains elusive. The determination of the structure of these RNPs is challenging due to their inherent complexity: these systems are dynamic, both in spatial conformation and subunit composition, which makes production, purification and crystallization also challenging.

We aim to contribute to the understanding of RNP biogenesis using structural biology to determine the structure of proteins involved in these processes. Based on our preliminary results, we have targeted several different aspects of RNP maturation which are tractable for structural studies. The project will focus on small protein complexes which are either autonomous building blocks of the RNP, or form during the RNP assembly line. We will also address protein/RNA complexes, when the RNA binding site is known. The structures determined will lead to functional hypotheses which will then be tested in vivo in the yeast model system. Our results will help understand the molecular basis of these genetic disorders and help the development of therapeutic drugs.