Noonan Syndrome (NS, OMIM 163950) is a condition characterized by typical craniofacial abnormalities, congenital cardiac defects, pulmonic stenosis, a wide spectrum of cognitive disorders causing a wide spectrum of mild/moderate mental retardation and learning disabilities (ranging from attention deficits to language impairments), multiple skeletal defects, cryptorchidism, short stature. More than 50% of the NS cases are caused by mutations in the PTPN11 gene, and 10-20% of the cases by mutations on SOS1 gene, encoding for two proteins, SHP2 and SOS1 respectively, that possess critical roles in the activation and regulation of the RAS/MAPK pathway. In both cases, mutations result in an abnormal gain-of-function, with mutations insisting on residues maintaining the proteins in an auto-inhibited state for SHP2 and mutations strengthening the interaction with Grb2 in the case of SOS1.
The project is based on the hypothesis that an effective therapeutic strategy for NS would be based on the recovery of the SHP2 and SOS1 normal functions. This aim will be achieved by studying the mechanisms of activation of SHP2 and SOS1 and designing small molecules to hijack the functions of these two proteins in the naturally occurring NS mutants.
The experimental plan is, therefore, based on the synergy between experimental and computational techniques focused on the understanding of the molecular details of the gain-of-function of SHP2 and SOS1 in NS. In parallel, small molecules stabilizing the auto-inhibited state of the two proteins will be selected via virtual screening and, subsequently, studied in vitro.
Overall, the proposed project has the goal to provide a mechanistic characterization of the most prominent mutations associated with NS and to identify one or more lead compound aimed at reducing the gain-of-function observed in the pathological conditions.
This research project is focused on the understanding of the molecular mechanisms underlying the Noonan Syndrome, a rare genetic disease. Whilst the molecular targets have been already identified, little is known about the molecular mechanism of the disease and no therapy is available to date.
Thanks to the synergy between molecular biology, chemical kinetics and drug design, this project has the potential to set up the discovery of small molecules that may pave the way towards a therapy for Noonan Syndrome.
The molecular mechanisms of Noonan Syndrome will be clarified through the characterization of SHP2 and Sos1, as well as their mutant forms that are reported to be responsible for this disease. In particular, the characterization of the C-SH2 domain of SHP2 has a great chance of success, considering data previously obtained for the N-SH2 domain of SHP2. Moreover, in the context of a different project, we have already cloned, expressed, and purified the SH3 domain of Grb2. The binding of this domain has been studied with a ligand that is similar to Sos1, the disordered tail Gab2, and these results confirm the feasibility of Aim2.
Overall, the project will tackle for the first time the mechanistic details of the gain-of-function of SHP2 and Sos1 for Noonan Syndrome mutants. It should be noted that no biophysical data are available to date on the molecular basis of this disease. Furthermore, the computational selection and in vitro testing of possible drugs to modulate the gain-of-function of SHP2 and Sos1 for Noonan Syndrome mutants represents a tantalizing possibility to relieve this disease. Whilst such a goal is relatively ambitious, it appears rather feasible as the experimental approach described in this project has been previously successful on similar small domain protein systems.