Ricerc@Sapienza

Fragile X Mental Retardation Protein (FMRP) is an RNA-binding protein (RBP) known to control different steps of mRNA metabolism, even though its complete function is not fully understood yet. It is well established that FMRP has a multi-domain architecture, characterized by the presence of 2 Tudor Domains (TD), three K Homology (KH) Domains and an arginine glycine-rich (RGG) box, feature that allows this RBP to be engaged in a large interaction network with numerous proteins, mRNAs or non-coding RNAs. Lack or mutations of FMRP lead to Fragile X Syndrome (FXS). Especially, beside the most common form due to the expansion of a CGG triplet located in the 5¿UTR of the gene encoding for FMRP (FMR1), there are Small deletions and single-nucleotide polymorphisms (SNPs) in critical domains of the FMR1 gene that are reported to cause FXS-like phenotypes. Interestingly, three of the four clinically relevant reported mutations fall in the KH domains, suggesting a particular important role for these domains in the physiological function of the protein. In this project we aim at characterizing the three KH domains that constitute the FMRP protein and their pathological mutants. In particular our goal is two-fold: 1) to solve the crystal structure of the three KH domain both in isolation and linked together and to unveil the structural rearrangements leading to cooperative RNA binding. The possibility to solve the structure of the KH domains in complex with the target RNA will also be evaluated. 2) to study the folding mechanism of these KH domains both in isolation and linked together and to characterize the folding intermediates (if any) which may be relevant in the reported ability of the KH domains to form ordered aggregates such as beta-amyloids. We believe that this study will be useful to a better comprehension of the features of the FMRP protein and will pave the way to further studies aimed at fighting FXS and FXS correlated pathologies.